Scientific explanations attempt to answer three questions: what we know (the ontological question), why it happens (the causal question), and how we know (the epistemic question; Osborne & Patterson, 2011). A scientific explanation includes three components:(a) a claim, (b) evidence, and (c) reasoning (McNeill, Lizotte, Krajcik, & Marx, 2006). Therefore, a claim itself is not a complete explanation because it lacks evidence and reasoning. These three components are further elaborated below:

  • Claim: The claim makes an assertion or conclusion that addresses the original question or problem about a phenomenon.

  • Evidence: The data from an investigation that support the claim. These data can come from an investigation that students complete themselves or from other sources, such as observations, reading materials, archived data, or from theoretical sources such as computer simulations. Data need to be appropriate, sufficient, accurate, and precise to support the claim. By appropriate, we mean that the data that are relevant to the problem and help determine and support the claim. Sufficient refers to providing enough data to convince another individual of the claim. Often, providing sufficient evidence requires using multiple pieces of data. By accuracy, we mean the degree of closeness of measurements of a quantity to that quantity’s true value. By precision, we mean the degree to which repeated measurements under unchanged conditions show the same results.

  • Reasoning: The reasoning links the claim and evidence and shows why the data count as evidence to support the claim. Often, in order to make this link, students must apply appropriate scientific principles or theories.

The process of constructing effective scientific explanations is considered an effective approach to constructing knowledge, as it moves beyond descriptions of observable natural phenomena into theoretical accounts of how phenomena unfold the way they do (Braaten & Windschitl, 2011; Chi, 2000; Chi & Bassok, 1989).

Unfortunately, students rarely have a lot of experience constructing explanations, nor have they been exposed to the explanation framework above; even less have they been asked to reflect on the nature of explanation in science. Therefore, to assess explanations and students’ ability to construct explanations, it might be necessary to provide scaffolds for students during formative assessment and later assess students without the use of scaffolds. One such scaffold is to make the claim-evidence-reasoning explanation framework explicit to students.

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