This article presents a model of collaborative inquiry for groups of science teachers who want to systematically improve their practice through analyses of student work. The five-phase APEX[superscript ST] (Advancing High-Leverage Practices by Examining Student Thinking) model is appropriate for students of all achievement levels. It focuses on high-leverage practices (e.g., pressing for evidence-based explanations) and longitudinal learning for both students and teachers over the course of a year. (Contains 2 figures and 4 online resources.)