How do students reason with existing knowledge and newly presented knowledge during science inquiry tasks

Combined= Paper Set Title: REASONING WITH THE KNOWLEDGE AT HAND: STUDENT REASONING IN CONTEXT RICH SETTINGS

&nb= sp;

Title: THE ROLE OF INSTRUCTION ON STUDENTS’ DEVELOPMENT OF EXPLANATIONS DURING INQUIRY T= ASKS INVOLVING THEORY ARTICULATION

Jerine Pegg, University of Idaho

Abstract=

This study examined stude= nt reasoning during inquiry tasks and the relationship between prior instructi= on and students’ ability to develop explanations that linked inquiry res= ults to scientific claims. Student= s’ written explanations were translated into causal representations and examin= ed for patterns in reasoning. The analysis highlighted issues related to students’ conceptualization of= the science concepts, their ability to apply the concept to variables in the investigations, and the nature of causal reasoning used in the explanations. Examination of = the instruction suggested that simplifications in the way the main concept was presented in activities leading up to the inquiry created difficulties for students when applying the concept in a more complex context.

Introduction

A primary = goal of inquiry instruction is for students to learn science by doing science. However, in order to make meaning = from inquiry investigations students must be able to develop explanations that l= ink evidence from the investigations with claims that further their understandi= ng of scientific concepts. The development of explanations requires reasoning about and justifying the relationships between evidence and theory. This is not a trivial task. Numerous studies have shown that t= he process of relating evidence to theories is often difficult for students (D= river et al., 1996; Kuhn, Amsel, and O’Loughlin, 1988). Studies of classroom inquiry lesso= ns have also shown that the nature of the task and teacher scaffolding can influence student success in developing explanations (Watson et al., 2004; Sandoval, 2003; Sandoval & Millwood, 2005).

The nature= of the explanations that students develop and the reasoning required to develop th= em depends upon the specific nature of the task in which students are engaged. Some tasks require students to generate theories from evidence (Kuhn, Amsel, and O’Lough= lin, 1988), use evidence to choose between theories (Samarapungavan, 1992), or a= pply theories to particular phenomena (Ohlsson, 1992). This study examines the latter of these.

Ohlsson (1= 992) describes the process of applying theories to particular phenomena as theory articulation, “…the activity of applying a theory to a particul= ar situation, to decide how, exactly, the theory should be mapped onto that situation, to derive what the theory implies or says about the situation.” The n= ature of the reasoning required to apply theories to particular phenomena differs from that required to generate theories or choose between competing theories. When applying theories to particular situations the theory is known and the evidence is constrained to a specific context. In this case, the reasoning requires an articulation of how the evid= ence relates to the theory and which aspects of the theory can explain the evidence. Since the theory is provided, the reasoning focuses more on identifying the relationships betwe= en the theory and the evidence and less on whether or not the evidence supports the theory.

This study examines the relationship between students’ reasoning about explanati= ons, the design of the inquiry task, and the nature of the classroom instruction leading up to the inquiry task. The goal of the study was to examine patterns in student reasoning about explan= ations, to identify challenges that students encountered when developing explanatio= ns, and to examine factors in the design of the task and classroom instruction = that may have influenced students’ development of explanations.

Specifical= ly, this study examined a Claims-Evidence inquiry task in which students developed a= nd conducted investigations in order to test a scientific claim. Claims-Evidence is an inquiry-based instructional strategy that uses a deductive approach to question generatio= n, in which scientific claims are used as springboards for student investigati= ons (Gummer, 2002; Thompson, 2003; Briley, 2003). In Claims-Evidence inquiry students are encouraged to consider how their questions, procedures, and conclusions relate to the claim they are testing. This encourages students to link t= heir evidence and explanations to the underlying science concepts rather than me= rely stating whether their data supports their hypothesis or not.

This paper describes the results of a case study of two teachers using a Claims-Eviden= ce task involving the application of the concept of conservation of momentum to the flight of water rockets. = The primary research questions addressed in this paper include the following:

· What is the nature of student reasoning about explanations during inquiry investigations involving theory articulation?

· How is prior instruction related to students’ ability to develop explanations during a Claims-Evidence inquiry investigation on the conservation of momentum?

Theoretical Framework

A framewor= k for identifying the components of explanations based on Toulmin’s argumentation model (1958) was used for this study. The framework focuses on three key components of explanations; claim, evidence, and reasoning. This framework has been used in pr= evious studies to examine the nature of student explanations and design instructio= nal scaffolds for inquiry-based curriculum (Sutherland, McNeill, & Krajcik, 2006; Kuhn & Resier, 2004).

This frame= work was used as a starting point for examining student explanations. However, since the nature of the t= asks examined in this study provide the claim for the students and narrowly constrain the nature of evidence that students use as support for the claim, the focus of the analysis was on the nature of the reasoning used to link t= he evidence and the claim.

Specifically, the nature of students’ causal reasoning in the explanations was examined. The causal relation= ships in students’ explanations were identified and examined for patterns.<= span style=3D'mso-spacerun:yes'> The forms of causality in student explanations were then further identified using the Taxonomy of Causal Mode= ls developed by Grotzer & Perkins (2000).

Research on student explanations suggests that the forms of causality that students use= to explain scientific phenomena can influence their understanding of scientifically accepted explanations. Grotzer (2003) suggests, “…students’ and scientists’ explanations often have a different underlying causal structure and that students’ relatively limited causal repertoire is = an important and systematic source of alternative conceptions in science” (p. 3). She suggests, “Developing sophisticated causal understanding is critical to develop= ing deep scientific understanding.” (Grotzer, 2003, p. 4)

Grotzer and Perkins (2000) developed the Taxonomy of Causal Models to characterize leve= ls of reasoning about the nature of causality in scientific explanations. This model consists of four dimens= ions: Mechanism, Interaction Pattern, Probability, and Agency. Levels of increasing complexity are identified and described within each dimension. The Interaction Pattern dimension = of this taxonomy was used as a framework for examining the nature of causality= in students’ explanations.

The Interaction Pattern dimension desc= ribes the nature of interactions between causes and effects. The simplest levels in this dimens= ion involve linear reasoning about the relationship between two variables, i.e.= A causes B. Higher levels invoke multiple unidirectional causes and/or effects (multiple linear causality), additional causes which may act as a barrier or catalyst (mediating causali= ty), two-way causality (interactive causality), simple causal loops (re-entrant causality), and causality that is constrained by a system of rules (constraint-based causality).

The Inquiry Task

The inquir= y task that was the focus of this study involved using water rockets to examine concepts related to the conservation of momentum. The water rocket inquiry came at t= he beginning of the school year following a one-week unit on inquiry and the nature of science and a three-week unit on force and motion.

The water = rocket inquiry was based on an activity that one of the teachers had been using fo= r about 10 years. Three years ago she decided to modify it into a Claims-Evidence Inquiry task. Prior to this modification, the st= udents were basically free to ask any question they wanted related to water rockets. Students asked quest= ions such as how the surface of the water rocket (i.e. covered with feathers or = oil) would influence the distance it traveled.&= nbsp; As the teachers began to focus this activity on specific scientific claims, they narrowed the questions that students investigated to ones which could be related to the claims and which could provide reliable data that c= ould be interpreted for patterns. =

Water rock= ets are constructed out of two-liter bottles that are filled with water and compres= sed air. The water rockets used in these classes were constructed by adding cardboard wings to a 2-liter bottl= e, placing clay on the nose of the rocket, and covering the entire assembly in duct-tape. An air compressor = was used to fill the rocket with compressed air to varying amounts. The rockets were launched at a 45-= degree angle and the horizontal distance traveled was measured.

The water = rocket inquiry consisted of three main activities; initial launches, a water rocket class example using a claim about force, and a water rocket student inquiry using a claim about momentum. During the initial launches, students observe= d as the teacher launched a plain 2-liter bottle, a water rocket with just air, = and a water rocket with some water in it. During the Water Rocket Class Example, the students worked as a clas= s to investigate the claim, “the amount of force affects the motion of an object.” For this inqui= ry the whole class investigated how the amount of force affects the motion of an object by changing the amount of air pressure in the rocket and measuring i= ts effect on the distance it traveled.

Following = the Water Rocket Class Example, the students were then given a second claim rel= ated to the conservation of momentum, “The conservation of momentum affects the motion of an object”. During the Water Rocket Student Inquiry the students worked in small groups to design and conduct the investigation. At the end of the inquiry, students individually typed up a final draft of their inquiry investigations.

In this in= quiry students were allowed to choose a question provided by the teacher or devel= op one of their own. The two que= stions provided by the teacher were, “How does the amount of water affect the distance of a water rocket?” and “How does the mass of the nose cone affect the distance of a water rocket?” The majority of students chose the question involving changing the amount of water in the rocket. This study reports only on student explanations related to this question.&nbs= p;

Students b= uilt their own rockets that would be used for data collection and were allowed to launch them multiple times. G= roups generally launched their rockets between 9 and 12 times in order to test multiple levels of their independent variable and conduct multiple trials at each level.

In order to explain the results of the inquiry investigations students needed to be abl= e to apply the concept of the conservation of momentum to the flight of the water rockets and to the independent and dependent variables in the investigation. In order to se= t the context for the later discussion of student explanations, I will briefly discuss the issues that need to be considered in developing these explanations. In general the conservation of momentum states, “the total momentum of an isolated system of bodies remains constant” (Giancoli, 1991). Rocket propulsion can be explained= in terms of the conservation of momentum.&nbs= p; Before the rocket is fired, the total momentum of the rocket plus fu= el is zero. As the fuel burns the total momentum remains unchanged. The backward momentum of the fuel, or water in the case of a water rocket, is balanced by the forward momentum of the rocket. Since momentum is defined as the p= roduct of its mass and its velocity, the conservation of momentum as applied to a water rocket can be represented as the mass of the water leaving the rocket= (m_w) times the velocity of the water leaving the rocket (v_w) is equal= to the mass of the rocket (m_r) times the velocity of the rocket (v<= sub>r) (m_wv_w =3D m_rv_r) (Figure 1).

&nbs= p; &= nbsp; &nbs= p; &= nbsp; &nbs= p; Explanatio= ns

&= nbsp;

Claim &= nbsp; &nbs= p; &= nbsp; &nbs= p; &= nbsp; Inquiry Results

Momentum of rocket moving forward

(m_rvr)

Momentum of water leaving the rocket

(m_wvw)

= “The Conservation of Momentum

= ;

= &nb= sp; = &nb= sp; = &nb= sp;

=3D

Figure <= !--[if supportFields]> SEQ Figure \* ARABIC = 1. Model for the devel= opment of explanations in the water rocket inquiry.

&= nbsp; &nbs= p; &= nbsp; &nbs= p; &= nbsp; &nbs= p;

* IV - m_w signifies that the independent variable is related to the mass of the water (m_w).

= ; DV – v_r signifies that the dependent variable is related to the velocity of the rocket (v_r).

In most ca= ses, the students investigating the water question found that increasing the indepen= dent variable resulted in an initial increase in the distance the rocket traveled and then a decrease in the distance as the independent variable was further increased. However, depending= upon the range of variables the students investigated and the accuracy with which they conducted their trials, some of the results only showed an increase or= a decrease.

Although w= ater rockets appear fairly simple, the physics behind their flight is extremely complex. To truly explain the results of the water rocket investigations would require complex mathematics and the inclusion of concepts, such as drag and the center of gravity of the rocket, concepts to which the students have not been introduced. However, the primary interest in t= his study is how the student explanations relate to the claim, rather than whet= her or not the explanations consider all possible factors influencing the resul= ts.

Developing= these types of explanations involves identifying the relationships between the results of the investigation and related science concepts. This involves two key components.<= span style=3D'mso-spacerun:yes'> The first component involves mappi= ng the specific application to the concept. In this case, this involves seeing the conservation of momentum in t= he context of water rockets as a relationship between the momentum of the wate= r leaving the rocket and the momentum of the rocket being propelled forward.

The second component involves relating the independent variable and dependent variable= to the science concept. When investigating the effect of changing the amount of water in the rocket, the independent variable is the amount of water in the rocket. Increasing the amount of water in = the rocket can increase the mass of the water leaving the rocket and therefore increase the momentum of the water leaving the rocket. In order for momentum in the syste= m to be conserved, the momentum of the rocket then also increases. Since the mass of the rocket is relatively constant, increasing the momentum of the rocket results in increasing its velocity, which results in increasing the distance it travels.

However, t= his relationship becomes more complicated as the amount of water in the rocket increases past about half full. As the amount of water increases, the volume available for pressurized air decreases and hence there is less stored energy available to push the water= out of the rocket. At some point,= not all of the water that is added is actually expelled from the rocket, decrea= sing the amount of mass leaving the rocket and therefore decreasing the momentum= of the water. This can still be explained using the conservation of momentum. However, the key is to focus on the amount of water that is actually expelled from the rocket, not just the amo= unt of water that is added.

This is a = fairly simplistic model of the application of the conservation of momentum to these investigations. This model ig= nores how changing the independent variables influence factors such as drag and center of gravity. Although t= his model is not complete, it is a representation of the model provided by the claim and prior instruction regarding the concept of conservation of moment= um and how water rockets work.

Methods

School Context

This study was conducted at a suburban middle sch= ool in the northwest. The school currently has an enrollment of 1065 seventh and eighth graders. Two teachers = were purposefully selected (Patton, 2002) for this study based on their experien= ce using Claims-Evidence Inquiry in their classrooms. The teachers are identified by the pseudonyms Anne and Brenda. B= oth teachers currently teach 8^th grade at the same school and have b= een using the same inquiry activities that they developed based on the Claims-Evidence approach for the last three years. One teacher taught five classes of= 8^th grade science and the other taught three classes. Observations were conducted = in one class of each teacher and written work was collected from students in all e= ight classes.

Data Sources<= /u>

Data sourc= es for this study included students’ written inquiry reports, videotaped classroom observations, teacher interviews, and instructional artifacts. At the end of the Water Rocket Stu= dent Inquiry, students submitted typed reports of their inquiry investigations. = The final inquiry reports were collected from the students in all eight classes. Digital photographs = were taken of all student inquiry reports and the analysis sections were transcr= ibed for further analysis.

Classroom observations were conducted during all classroom sessions of the Water Rock= et Inquiry, including the initial launch, the Water Rocket Class Example, and = the Water Rocket Student Inquiry. During these sessions the classes were observed, videotaped, and two focus groups of students in each class were audiotaped. The researcher also took field not= es during the classroom observations. <= /span>

Semi-struc= tured interviews were conducted with each teacher prior to and following the water rocket unit. The pre-inquiry interview addressed the teachers’ beliefs about inquiry teaching, the teachers experience with the activity and the Claims-Evidence Approach, the= ir understanding of the relationship between Claims-Evidence and student understanding of science concepts and inquiry, and the teachers’ instructional goals f= or the unit and the activity. The post-inquiry interview probed the teacher to reflect on how they thought the water rocket inquiry went in terms of their instructional goals and students’ ability to link the claim to their results, what components= of the inquiry students engaged in reasoning about the science concepts, and a= ny changes they would make to the inquiry in the future.

The teache= rs were also interviewed about the nature of the instruction that the students experienced prior to starting the water rocket inquiry. Prior to the interview, the teachers’ lesson plans, handouts, and student journals were examined = to develop a chronological description of the instruction that occurred prior = to the water rocket inquiry. Bas= ed on these artifacts, the researcher wrote general descriptions of each activity= and noted questions about the nature of the instruction. During the interview the teachers = were asked to describe the nature of the content (i.e. Newton’s first law, second law) and the inquiry (i.e. asking questions, making predictions, supporting predictions, observing phenomena, collecting data, measurement, graphing, identifying patterns, formulating explanations, examining alterna= tive explanations) present in each activity.&nb= sp; The teachers were also asked to clarify any questions that the researcher had about the nature of the activities or their classroom presentation. Both teachers w= ere present during this interview and were asked to note any cases in which instruction varied between their classes.&= nbsp;

Data Analysis

The analys= is sections of students written inquiry reports from 8 classes (n=3D184) were examined to identify the nature of student reasoning about explanations. Written reports from students investigating the water question that specifically linked the claim to the results (n=3D40) were transcribed and causal representations were created to examine patterns in student reasoning.

Causal representations were created by simplifying the written explanations into t= heir key components. The key varia= bles in the explanations were identified (i.e. water, mass, velocity, momentum, distance) and links between these variables were noted. A representation system was create= d to identify important components of the students’ explanations. Figure 2 shows an example of how the students’ written analysis sections were = translated into causal representations. = The details of the methodology used in this analysis will be described in future papers.

Key: = a) =3D Expl= anations for increasing distance &n= bsp; w =3D water leav= ing the rocket

= b) =3D Explanations for decreasing distance &= nbsp; r =3D rocket

= à =3D Connection between two variabl= es = a =3D air pressu= re

Italics =3D Implied bu= t not explicitly stated &n= bsp; g =3D ground

&nbs= p; = [ ] =3D Supporting Statements or Qua= lifiers

Sample Analysis Section

“The momentum was conserved a= nd it affected the motion of the water rocket.&n= bsp; When more water was a= dded there was more mass. More= mass means there will be more mom= entum (unless you add too much). The water rocket went farther from 0 ml to 500 ml of water, then it didn’t.”

Causal Representation of Student Explanation

a) &= nbsp; More Water à More Mass à Mo= re Momentum = More Distance

b) &n= bsp; = ; &n= bsp; = ; [unless too much mass] = ; &n= bsp; = ; Less Distance

Figure . Example of translation from written explanation to causal relationships

In order to examine patterns in the student explanations, the elements of each causal representation were then organized into columns so that the links between t= he independent variable (amount of water or mass of the rocket) and the depend= ent variable (the distance the rocket traveled) could be identified. The causal representations were th= en sorted into similar groups depending upon the question they were investigat= ing and the links they included. = This allowed for the identification of patterns in the students explanations. Based on these patterns, iss= ues related to student reasoning about explanations were identified.

Analysis o= f the data related to classroom instruction began by transcribing teacher discour= se from the classroom observations and interviews. The multiple data sources, includi= ng teachers’ classroom discourse, teacher interviews, and instructional artifacts were then coded based on the issues that had been identified in t= he student explanations.

Results

The result= s will be presented in two sections. First, the patterns in student explanations will be discussed. Then the relationship between stud= ent reasoning about explanations and classroom instruction will be examined.

Student Explanations

Examinatio= n of patterns in the student explanations highlighted three issues related to student reasoning about explanations: (1) conceptualization of the concept,= (2) ability to apply the concept to specific phenomena, and (3) the nature of t= he causal reasoning required in the explanation.

Concep= tualization of the Science Concept - Momentum versus Conservation of Momentum

Applying the concept of conservation of momentum to the water rocket investigations involves seeing the water rocket as a system in which the momentum of the system is conserved. In this system, the momentum of the water leaving the rocket is equal to the moment= um of the rocket being propelled in the opposite direction. However, only 8 of= the 40 students (20%) made a distinction between the momentum of the water and = the momentum of the rocket.

Most of the students discussed how adding more water to the water rocket gave it more momentum. For example, “As the amount of water increased, the distance traveled by the rocket increased until it got to a certain point, then it decreased. Therefore, as the amount of water applied to the water rocket increased, its momentum also increased until it= got to a certain point then it decreased.” [TB6004] However, they did not discuss this= in terms of the conservation of the momentum of the system.

<= span style=3D'text-decoration:none'>

Applyi= ng the Concept of Conservation of Momentum to Water Rockets - Linking the Independ= ent Variable, Dependent Variable and the Science Concept

Looking at= the links that students make between the independent variable, the dependent variable and momentum allow for a better understanding of how they are rela= ting the evidence to the claim. Re= lating the independent (IV) and dependent variables (DV) to momentum requires an understanding of how changing the IV and DV relate to changing the mass or velocity of either the water or the rocket. Students varied in the extent to w= hich they made these links explicit. Figure 3 shows the percentage of students that attempted to explain = the relationship between the IV, DV and momentum.

Independent Variable (amount of water)

· = ; No explanation of the relationship between adding water and changing momentum (40%)

· = ; Identified the relationship between adding w= ater and change in momentum as one of changing mass (33%)

· = ; Identified the relationship between adding w= ater and change in momentum as one of changing the force, velocity, o= r acceleration of the water (30%)<= /p>

Dependent Variable (distance of rocket)

· = ; No explanation of relationship between chang= ing momentum and changing the distance (92.5%)

· = ; Identified the relationship between changing momentum and change in distance as one of changing the mass of the rocket (2.5%)

· = ; Identified the relationship between changing momentum and change in distance as one of changing the velocity or accelerati= on of the rocket (5%)

= Figure 3. Relationship between IV, DV, and momentum in student explanations (n=3D40, percentages m= ay add up to more than 100%, because some students identified mass and force, velo= city or acceleration)

Sixty perc= ent of the students attempted to identify the relationship between changing the am= ount of water and a change in momentum. Thirty three percent stated that this relationship had to do with changing mass and 30% stated that it had to do with changing the force or velocity of the water.

In contras= t to student explanations for the relationship between the independent variable = and momentum, few students explicitly described the relationship between changi= ng the momentum and resulting changes in the distance the rocket traveled. Only 7.5% of the students describe= d how changing the rockets momentum resulted in a change in its distance.

Nature of Students’ Causal Reasoning about Explanations

A third issue related to students’ explanations involved the nature of = the causal reasoning evident in student explanations compared to the forms of causal reasoning required to accurately explain the relationship between the claim and the results.

Reasoning about conservation rules, such as in the conservation of momentum, involves constraint-based causality. In constraint-based causality, the behavior of the system reflects a set of constraints that the system obeys. However, the level of causality required to reason about the system depends on the phenomena that the explanation is being applied to (Grotzer = and Perkins, 2000). Therefore, the level of causality in student explanations will be discussed with particular reference to the actual results the students were explaining.

For the water question, some students had results that showed an increase and t= hen decrease in distance, whereas others only showed an increase or only a decrease. Depending upon these results, the reasoning required ranged from simple linear causal reasoning = to multiple linear causal reasoning with mediating factors. When changing the amount of water = in the rocket, the amount of space available in the rocket for air acts as a media= ting factor on the relationship between increasing the amount of water in the ro= cket and the distance the rocket travels.

Students t= hat only tested values of water from zero to about half full had results that showed only a positive correlation between the amount of water and the distance the rocket traveled. These result= s can be easily explained using simple linear causal reasoning. Figure 4, Example A, shows an exam= ple causal chain that could explain the positive correlation between the amount= of water and the distance traveled.

Nine of the student work samples had results that only showed an increase in the distance the rocket traveled. All of the student explanations in this group employed single causal chains like example A. All of these explanations related the increase in water to an increase in momentum and t= hen a resulting increase in distance.

Example A: Model Causal chain for the increas= e in distance:

More Water à More Mass (w) = à More Momentum (w) à More Momentum (r) à

More Velocity (r) à More Distance

Example B: Model Causal chain for the decreas= e in distance:

More Water à Less Volume (a) à Less Mass (w) = à Less Momentum (w) à

Less Momentum (r) à Less Velocity à (r) à Less Distance

More Water à Less Volume (a) à Less Mass (w) = à More Mass (r) = à Less Velocity (r) à Less Distance

Figure 4: Model Causal Chains for the Amount of Water Question

(w =3D water leaving r= ocket, r =3D rocket, a =3D air, i.e. Mass (w) =3D Mass of water leaving rocket)=

&nbs= p;

Three of the students had results that only showed a decrease in the distance traveled. Two of them used li= near causal reasoning to explain the relationship between less water escaping the rocket to a decrease in the momentum resulting in a decrease in the distance traveled (TB6027 and TB6023). These explanations were similar to Example B in Figure 4. These students also employed media= ting causes to explain the relationship between increasing the water and having = less momentum. They suggested that= as the mass of the water increased not all of the water could escape and there= fore the momentum decreased (figure 5). <= /span>

<= /o:p>

More Wat= er à Less Momentum = à = &nb= sp; = Less Distance [TB6027]

[not a big enough exit hole for all of the water= to escape]

More Mass/not enough f= orce à = &nb= sp; = &nb= sp; Less Distance

Figure 5: Causal representation of student explanation for decreasing distance

The third student identified a relationship between adding water and changing momentum, but did not describe whether it increased or decreased the moment= um or how it related to the decrease in distance (TB5015).

The majori= ty of work samples (n=3D28) had results that showed an increase and then a decrea= se in the distance that the water rocket traveled. In these cases, simple linear caus= al reasoning was no longer sufficient to explain the results. Of these work samples, 21 of the students attempted to explain both the increase and the decrease in distanc= e.

Students p= rimarily used multiple lines of reasoning and invoked mediating causes involving the decreasing space left for air in the bottle as the amount of water was increased. However, the major= ity of students (n=3D18) only explained the increase in terms of momentum and then employed alternate theories to explain the decrease in distance. Some of the students explained tha= t the decrease was due to less water being pushed out, but did not relate this to= a decrease in momentum of the water or the rocket. The rest of the students related t= he decrease in distance to an increase in mass, a need for more force, or a decrease in acceleration. Two examples of these explanations are shown in figure 6.

1. = a) More Water à = ; &n= bsp; More Momentum = ; &n= bsp; = ; &n= bsp; More Distance

b) More Water à More Mass/Less Volume (a) &= nbsp; &nbs= p; &= nbsp; &nbs= p; &= nbsp; Less Distance

[Not enough room for air pressure]

[TB6004]

2. = a) <1,500ml More Mass à More Momentum à More Acceleration (r= ) More Distance

b) >1,500ml &= nbsp; [Until mass gets too great for the force] à = &nb= sp; Less Distance

[TA2012]

Figure 6: Causal representations of student explanations for increase then decrease in distance

Relationship between Ins= truction and Explanations

Analysis o= f the instruction showed that the students had been exposed to the concept of the conservation of momentum prior to conducting the inquiry. In the prior instruction, they had= taken class notes, read a section from the textbook, and conducted a lab on the conservation of momentum (the Ramp of Ramming Lab). However, close examination of the = nature of the concept presentation in the prior instruction and the requirements f= or applying the concept in the context of the inquiry suggested distinct differences that may have hindered students’ ability to reason about = their results and develop fully accurate explanations.

Concep= tualization of the Science Concept

The law of conservation of momentum can be applied to collisions between objects and certain types of explosions, such as in rocket propulsion. The prior instruction regarding the conservation of momentum focused primarily on the conservation of momentum = for two colliding bodies.

In the jou= rnal notes that students took there were two statements relating to the conserva= tion of momentum. The first descri= bed what happens when one object collides with another object, “When a mo= ving object hits another object, some or all of the momentum of the first object= is transferred to the other object.”&nb= sp; The second statement suggests consideration of the vector aspect of momentum, “When you get mass moving in one direction, the momentum is transferred in the opposite direction.” This description is applicable to = the conservation of momentum for explosions, but is overly simplified for an application to collisions.

The textbo= ok reading also focused primarily on the conservation of momentum for colliding objects. It described how mom= entum is conserved when a moving object “hits” another object, or any= time “two or more objects interact”. The Ramp of Ramming lab that the students conducted on the conservation of momentum also focused only on the transfer of momentum for colliding objects. In this lab, students ran a cart d= own a ramp and recorded how this affected the distance that a ball hit by the cart traveled. <= /p>

In the pri= or instruction, the conservation of momentum was often described as a linear cause-effect relationship in which one object collides with another causing its momentum= to change. The presentation of t= he conservation of momentum was rarely described as a “system” in which the momentum stays constant. In the prior instruction the students were primarily applying the concept of the conservation of momentum to collisions, whereas in the Water Rocket Inquiry they were required to apply the concept to explosions. Applying the concept of conservati= on of momentum to explosions requires a more complex understanding of the concept than does applying it to collisions.

Applyi= ng the Concept of Conservation of Momentum to Water Rockets

Reasoning = about the results of the Water Rocket Inquiry requires that students identify the relationship between the concept of momentum and the independent and depend= ent variables. Students varied in= the extent to which they explicitly connected the concept of conservation of momentum to the independent and dependent variable of the investigation. The majority of students attempted= to connect the change in the independent variable (amount of water in the rock= et) to the concept of momentum, but very few students attempted to connect the change in the dependent variable (distance the rocket traveled) to momentum.

Analysis o= f the instruction showed that the teachers provided extensive modeling during lar= ge group discussions of explanations that clearly linked the scientific concep= ts to the independent and dependent variables in the investigation. In these discussions, the teachers probed students to elaborate on their explanations in order to more explici= tly connect the scientific concepts to the independent and dependent variables = of the investigation. This instr= uction appeared to support students in recognizing this as a key component of their explanations.

However, s= tudents were much more likely to make this connection explicit in regards to the independent variable than the dependent variable. Examination of the prior instructi= on related to momentum suggests an explanation for this. In the prior instruction the teach= ers provided students with experiences that modeled the relationship between momentum and changing mass and velocity in the Ramp of Ramming Lab. However, in this lab the relations= hip between momentum and the distance an object traveled was not explicitly discussed. The distance the b= all traveled was used as an indicator of momentum without explicitly discussing the rela= tionship between momentum and distance traveled.&nb= sp; Since the relationship between momentum and distance traveled was implied as a direct relationship in the prior instruction, students may not have felt a need to explain this connection in the analysis of their result= s or they may not have understood this relationship and therefore not been able = to explain it.

Nature= of Students’ Causal Reasoning about Explanations

In the Wat= er Rocket inquiry all of the students were investigating the same claim. Howev= er, the causal reasoning required to explain the results in terms of the claim varied depending upon the question that was being investigated and the data that was actually collected. = The cognitive complexity of the reasoning that was required to develop explanat= ions for the results was not the same for all students. Based on the Taxonomy of Causal Mo= dels (Grotzer and Perkins, 2000), the reasoning required to connect the results = to the claim ranged from simple linear causal reasoning to constraint-based reasoning.

Students w= ho investigated the water question and collected data which only showed an increase or a decrease in the distance the rocket traveled could use simple linear causal reasoning to explain their results in terms of the conservati= on of momentum. Students who investigated the water question and collected data which showed an initial increase and then a decrease in the distance the rocket traveled were requi= red to incorporate mediating causes and multiple lines of causal reasoning.

In the Wat= er Rocket Inquiry, a few students (n=3D5) investigated the effect of changing the mas= s of the nose on the distance that the rocket traveled. For this question, linear causal reasoning is not sufficient to reason from the results to the claim. In this case constraint-based reasoning is required. Constraint-based reasoning is a mo= re cognitively complex form of reasoning than simple linear reasoning (Grotzer= and Perkins, 2000). The limited n= umber of students investigating this question limits conclusions that can be drawn