Flexible classrooms are designed to support active learning through movable tables and chairs that can be rearranged into different layouts and through technology such as wall-mounted monitors and whiteboards. This paper investigates how instructors experienced with active learning use the furniture and technology of a flexible classroom to facilitate active learning. We present a case study of one flexible classroom across courses at different levels of the engineering curriculum, analysing how the instructors used the classroom to implement nine strategies for facilitating active learning. Our findings provide many examples of how the flexible classroom allowed instructors to easily walk around the room and interact with students in a way that better facilitated active learning. The flexible classroom also supported the instructors in developing a routine for active learning and designing activities to better engage students. We conclude by describing evidence-based recommendations for flexible classroom professional development informed by our analyses.