Classroom management remains a challenge for many teachers. The approach and delivery of professional development (PD) in classroom management may determine how well teachers are able to apply evidence-based approaches in their classrooms. We use existing literature to identify the key features that make in-service PD effective and present them as the defining features of a recently developed PD program, "Classroom Management in Action," which blends online technology, evidence-based practice in positive behavior support, video modeling, self-paced/step-by-step activities, and tools for aiding and measuring fidelity and behavioral outcomes. We report results from studies documenting the program's social validity, the psychometrics of its online behavioral assessment tool, and its effectiveness based on an initial pilot test using a randomized controlled field trial involving 101 classrooms. We offer recommendations for future research on PD in classroom management and implications for policy and practice.