Teaching observations are crucial for our development as teachers, and they are also an important form of departmental service. When seasoned instructors offer to observe new instructors, they take on an important role as a mentor. But even senior instructors can benefit immensely from inviting peers to observe a class they have taught frequently. Peer observations that focus on growth are formative, rather than summative. This means observers are not conducting a formal evaluation that often results in letters for the observee’s teaching portfolio or annual review. Rather, this becomes an opportunity to set goals for future teaching, foster mentorship, and solicit constructive feedback. The Teaching Observation Toolkit makes transparent the processes for conducting a productive and collaborative formative observation, including the necessity of pre- and post-observation meetings. It includes a guide to conducting formative observations, lesson plan and note taking templates, and an observation rubric that can both focus the observation and guide conversations about instructor preparation, facilitation of learning, and engagement.