Have you ever had students respond, “I don’t know. It just did,” when asked to analyze and interpret their classroom lab results? We all want our students to “think like a scientist,” but often they fall short in connecting the dots between the lab results and the science concepts. Claim-Evidence-Reasoning or CER is a writing strategy that can develop a student’s analytical thinking and argumentative writing skills to turn that “I don’t know” into “aha, so that’s why we got those results in the lab.”