<p>Scientifically literate citizens need to know how to use scientific ideas and crosscutting concepts to determine what counts as evidence to support claims. Research is needed to develop an understanding of how to support students in the endeavor. This study investigates how to support students in developing usable knowledge that they can apply in new situations. Assisting students in developing this usable knowledge includes helping them to make claims and in supporting them to connect scientific ideas with data to show why the data counts as evidence to justify their claims, a critical aspect of scientific reasoning. In this study, learners constructed four iterations of a scientific explanation across time to explain a complex phenomenon, the water quality of a local stream. We examine learners’ emerging understanding of this complex phenomenon as they collect and analyze water quality data. Research reported here explores 1) the change in the level of sophistication of students’use of scientific ideas and crosscutting concepts to make sense of and explain why data counts as evidence, and 2) if and how students adjust their claims over time, as new and sometimes contradictory evidence is obtained. The research shows various trends of student knowledge development over the course of four iterations of the evolving explanation. Results indicate statistically significant differences in students’ understanding of using crosscutting concepts to connect scientific ideas with data to serve as evidence to explain the phenomenon. Results indicate no statistical significance for scientific ideas or connections to scientific ideas as predictive of claims that students made. The research indicates that using an evolving explanation within a 3-dimensional learning environment assists students in developing useable knowledge. Challenges arose when students needed to adjust claims when confronted with new, contradictory evidence.</p>