Classroom assessment practices have shifted from a focus on checking for students' understanding of memorized material to examining their conceptual understanding as they engage in activities that involve scientific reasoning, inquiry skills, performances, and products. Inquiry-based science has shifted instruction away from teacher-centered, didactic teaching to student-centered, active learning. This shift is naturally accompanied by a need for formative assessment strategies that help students and teachers determine the learning that is occurring along the way. In this article, the authors discuss several assessment strategies that teachers can use and adapt for inquiry-based science units, using the example of a weeklong fifth-grade unit about owls and owl pellets. These strategies, appropriate for middle to upper-elementary level students, actively involve students and provide them with the opportunity to self-assess their own learning. (Contains 7 figures and 5 online resources.)