There is a growing need for valid and reliable measures to monitor the efficacy of undergraduate science, technology, engineering, and mathematics (STEM) reform initiatives. The Classroom Observation Protocol for Undergraduate STEM (COPUS) is a widely used tool originally designed to measure the presence of overt instructor and student behaviors. It has subsequently been used to characterize instruction along a continuum from didactic to student centered, and more recently to categorize instruction into one of three styles. Initiatives focused on professional development often support instructors' progression from didactic to student-centered styles. There is a need to examine COPUS instructional styles in terms of behaviors that research has shown to improve student learning. Formative assessment is a research-based practice that involves behaviors accounted for by the COPUS (e.g., posing a question). We qualitatively compared the formative assessment behaviors in 16 biology class sessions categorized into each of the three COPUS styles. We were unable to detect differences in formative assessment behaviors between the COPUS styles. Caution should be taken when interpreting COPUS data to make inferences about the effects of reform efforts. This study underscores the need for additional measures to monitor national reform initiatives in undergraduate STEM.