The authors outline the application of latent class analysis (LCA) to classroom observational instruments. LCA offers diagnostic information about teachers' instructional strengths and weaknesses, along with estimates of measurement error for individual teachers, while remaining relatively straightforward to implement and interpret. It is discussed how the methodology can support formative feedback to educators and facilitate research into the associations between instructional practices and student outcomes. The approach is illustrated with a secondary analysis of data from the Measures of Effective Teaching study, focusing on middle school literacy instruction. [This report was published in "Educational Researcher" (EJ1068117).]