Constructing explanations of complex phenomena is an important part of doing science and it is also an important component of learning science. Students need opportunities to make claims based on available evidence and then use science concepts to justify why evidence supports the claim. But what happens when "new" evidence emerges for the same phenomenon? The "claim" portion of the "claim, evidence, and reasoning" explanation framework is viewed as the most accessible to students. When new evidence suggests that students adjust their current thinking however, do students incorporate this new information and modify their claims? This research utilized a time series research design to explore how students modify their claim over four iterations of one explanation, termed an "evolving explanation." As new data were collected and analyzed to provide additional evidence, students needed to evaluate their current claim to see if it took into account all available evidence. This research explores that process including the supports that the teacher provided and the challenges that students faced in developing one claim, over time. The findings indicate that many students face challenges adjusting their claims when new, conflicting evidence emerges, even with class discussion, teacher feedback, and written scaffolds. Several possible reasons exist to account for this challenge. Students may (1) ignore new evidence, (2) find "undoing" their initial idea too cognitively demanding, or (3) simply not have any similar experience from which to build. Providing students with experiences of writing evolving explanations reflects what scientists do, while simultaneously preparing students to become more scientifically proficient.