In this article, the authors describe how they used formative assessments to ferret out possible misconceptions among middle-school students in a unit about weather-related concepts. Because they teach fifth- and eighth-grade science, this assessment also gives them a chance to see how student understanding develops over the years. This year they used the formative assessment probe "Wet Jeans" from "Uncovering Student Ideas in Science: 25 Formative Assessment Probes" (Keeley, Eberle, and Farrin 2005). (Contains 4 figures.)