tigations.² The IQWST units are designed to teach both 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. The framework includes three components:

Thus, the curriculum helps students make sense of the phenomena under study (claim), articulate that understanding (evidence), and defend that understanding to their peers (reasoning).

As described earlier, part of the Struggle for Survival unit includes a two-week project in which students investigate a database holding information about the finch population on the Galapagos Islands. Students work in pairs in order to interpret the computer data and determine why so many finches died during the dry season of 1977 and why some were able to survive. The scientifically supported explanations for this question use data to identify which trait variations enabled birds to differentially survive the drought. For example, one response could state that the birds that survived the drought had longer beaks, which enabled them to crack the harder seeds that also survived the drought. Another plausible argument consistent with the data (but scientifically less accurate) could be that the birds that weighed more had fat stores that made them better able to survive the food shortage resulting from the drought.

Below is an excerpt from a student group presentation in which students use the claim-evidence-reasoning framework to reflect on their analysis and explain their current thinking about the investigation.