Classroom action research (CAR) represents a midpoint between teacher reflection at one end and traditional educational research at the other. CAR is a process in which a teacher identifies problems in the context of his or her own classroom and then engages in investigative methods to address the problems. Teachers sometimes shy away from CAR, due to their lack of training in research methodology, time constraints, and the fact that not all schools value or support such a scholarship of teaching and learning. I show how cultural-historical activity theory (CHAT) could be used as a practical lens when engaging in CAR, and how this could help biology teachers become more reflective practitioners by using a rigorous tool to analyze data. Third-generation CHAT is explained and the reader is shown, through a practical example, how research findings could be analyzed and interpreted through a CHAT lens.