DEFENDING EVIDENCE-BASED SCIENTIFIC EXPLANATIONS

Constructing scientific explanations is an essential aspect of engaging in scientific inquiry in classrooms (Driver, Newton, & Osborne, 2000; Sandoval, 2003). The IQWST units are designed to teach scientific principles and the scientific practices of constructing and defending explanations, by providing students and teachers with a framework that clearly defines this complex practice. This framework includes the three components of claim, evidence and reasoning. Our study analyzes student work using this instructional framework, in light of the curricular goals we would like students to achieve: 1) make sense of the phenomena under study, 2) articulate that understanding and 3) defend the understanding to one’s peers. Through this analysis, we find that the instructional framework supports students in using evidence to make sense of the phenomenon under study but that the students are not clearly articulating the relationship between the evidence and inferences, in their explanations. We conclude the paper with possible design strategies for supporting students as they use differentiated evidence and inference to defend their explanations. INTRODUCTION The goal of science is to construct, evaluate, and refine explanatory models (Duschl, 1990). In the last two decades, two related themes of science education reform have emerged from this focus on science as explanation. First, reforms call for conceptual understanding and reasoning about mechanisms to be cast as the goals for science learning (Linn, Songer, & Eylon, 1996; Smith, 1991; Strike & Posner, 1985). Second, scientific inquiry is thought to be core to science learning, in which students develop and argue for explanations through their own investigations (AAAS, 1990; Blumenfeld et al., 1991; Duschl, 1990; NRC, 1996). In this literature, explanations are both the goal of the activity and the means to get there – that is, students construct explanations in order to understand the phenomenon and as a motivation and guide for engaging in the inquiry process (de Vries, Lund, & Baker, 2002; Driver et al., 2000; Duschl, 2000; Osborne, Erduran, & Simon, 2004; Sandoval & Reiser, 2004). As each of these authors discuss, constructing explanations is a complex practice that incorporates many different types of activities. Moreover, constructing and discussing explanations is hard for students – it requires that they use their evidence to evaluate and revise their claims, connect their evidence to the relevant scientific principles and effectively communicate these understandings. Current reform efforts attempt to characterize the nature of the challenges that students face when constructing and communicating explanations and to design supports that address these challenges (e.g., Hogan & Corey, 2001; Scientific Explanations Leema Kuhn and Brian Reiser 2 Jimenenez-Aleixandre, Rodriguez, & Duschl, 2000; Palincsar, Anderson, & David, 1993; Sandoval & Reiser, 2004; Toth, Suthers, & Lesgold, 2002). This study is part of the IQWST research and design initiative in which we design, enact and research middle school science curricula designed to support scientific practices of explanation and argument as learners engage in project-based investigations (Krajcik & Reiser, 2004; Reiser, Krajcik, Moje, & Marx, 2003). The IQWST team has currently created two middle school units – the chemistry unit How can I make new stuff from old stuff (McNeill et al., 2004), and the biology unit What will Survive (Bruozas et al., 2004). Part of this process was to create an instructional framework that supports learners in using evidence to construct and defend their scientific explanations, in both content areas. This framework was designed to support students as they engage in both the inquiry process of figuring out what is going on and the act of communicating this understanding. In this paper, we examine whether and in what ways students working with the IQWST biology unit use the instructional framework in their written explanations, and how these responses reflect the different aspects of constructing and communicating an explanation. In this work, we are attempting to understand the different aspects of producing and communicating a scientific explanation, the challenges that students face when doing so and how curriculum materials can support this process. UNPACKING THE PRACTICE OF EXPLAINING Examining the science education research and philosophy of science literature reveals the many different aspects and meanings of the practice of “explaining. ” At the most general level, we can examine what an explanation is – the product. From this perspective, an explanation is commonly defined as a causal account of how or why something occurred (e.g., Horwich, 1987). Science education researchers add to this more general definition by specifying that the causal accounts must be linked to evidence (Bell & Linn, 2000; Duschl, 2000; Osborne et al., 2004; Sandoval & Reiser, 2004). Nagel (1979) also focuses on the product of explaining. As well as emphasizing the importance of evidence, Nagel adds a taxonomy of explanation types – each of which uses different reasoning patterns to answer the question “why”: deductive, mechanistic, genetic and probabilistic. A second theme that emerges out of this work is a focus on the process of explaining. For example, De Vries et al. (2002), highlight the sense-making aspects of the practice, stating that “in order to explain, students have to externalize, but also to clarify, organize and restructure their Scientific Explanations Leema Kuhn and Brian Reiser 3 knowledge” (p. 68). Similarly, science standards (AAAS, 1990; NRC, 1996) emphasize the importance of having students use logic and evidence to develop explanations. Current views of science emphasize the role of a scientific community in the scientific knowledge building process, in which scientists propose and thereby test their ideas in their community (e.g., Duschl, 1990). This perspective on science as knowledge building in a community adds to the process and product based definitions by suggesting the importance of examining the social interaction aspects of constructing explanations (Herrenkohl & Guerra, 1998; Hogan & Corey, 2001; Scardamalia & Bereiter, 1994; Tabak & Baumgartner, 2004). De Vries et al. (2002) provide a useful framework to characterize these various elements of explanation, and described three potential contexts in which students could explain: First, students explain an occurrence to themselves – using the explanation as a sense making opportunity. Second, explanations are a social, communicative practice in which students share their understandings with one another. Finally, scientific ideas need to be tested in a social process of discussion and debate. De Vries et al. (2002) used the term “argumentation” to discuss explanations that are used in this persuasive, disputed context in which individuals are attempting to convince one another of their explanations. The IQWST team drew from each of these aspects and definitions of “explanation” to construct our instructional supports for the practice of constructing and communicating explanations (Bruozas et al., 2004; McNeill et al., 2004). The IQWST materials are designed to support three related curricular goals encompassed in the single practice of constructing and defending scientific explanations: (1) using evidence and general science concepts to make sense of the specific phenomena being studied (2) articulating these understandings in terms of the evidence gathered and relevant scientific ideas and (3) defending these understandings by explicitly connecting the specific evidence and general principles about the relevant scientific concepts to the knowledge claims. While each of these curricular goals are related, it is important to recognize their individual importance. First, students must make sense of the phenomena they study and experience. For example, in the IQWST biology unit, students are asked to use population and trait variation data to explain why some birds survived a drought while others did not. Doing this in a way that is consistent with scientific inquiry requires that students connect the scientific ideas, to which they are being Scientific Explanations Leema Kuhn and Brian Reiser 4 introduced, with the evidence they have collected, and their prior conceptions and experiences (Driver et al., 2000; Jimenenez-Aleixandre et al., 2000). This process is a key component of students developing a deep-content understanding, rather than a more surface memorization of facts (Coleman, 1998). The second sense of “explain” seen in the literature is to articulate one’s understandings about what or why an event occurred. That is, students must put their understandings into a coherent expression in discourse. Lemke (1990) argues for the importance of this focus on communication, concluding that one understands something only when they understand the ways in which the idea can be communicated. Other science education research agrees with this focus on communication — it is through communication that students have opportunities to identify the strengths and weaknesses of their understandings (Bell & Linn, 2000; de Vries et al., 2002; Sandoval, 2003; Scardamalia & Bereiter, 1994). Thus, this second goal of communicating one’s understandings through scientific explanations is one step in the development of communitysupported reflection on the students’ developing understandings. Finally, moving beyond an articulation of understandings, students should engage in persuasive discourse, defending their explanations. Scientific inquiry is fundamentally a knowledge building process in which explanations are presented to the community so they can be critiqued, debated and revised. Thus, in order to engage in similar scientific knowledge-building practices, students must participate in the collaborative, persuasive discourse of consensu