Active learning generally increases student achievement, but not all implementation strategies exhibit the same magnitude of gains. In this study, we developed an instrument to characterize how active learning is carried out in a classroom and correlate scores on this instrument with differences in student performance. Although multiple tools exist for documenting active learning, none have been used to explain variation in student achievement. Our instrument documents not only the amount of time students are active in the classroom, but also how closely an instructor’s use of active learning aligns with best practices from the education research literature. We are in the initial phase of testing which elements of the rubric are correlated with student exam achievement. To capture a range of classroom types, we are using archival footage of 27 introductory biology instructors. We will use principle components analysis and linear models to identify which elements of the rubric best predict student performance after controlling for variability in student ability and exam challenge between classes. With this baseline data, we will be able to discuss the use of the rubric to help faculty assess the effectiveness of their in-class instruction strategies.