Teacher professional development (PD) is widely pursued as a critical component of overall school improvement. However, it is frequently ineffective at changing teaching practice or impacting student outcomes. While online PD has the potential to greatly expand access to high-quality PD, questions remain about the extent to which online PD can be effective. This study examined the instructional design of an active learning asynchronous online PD short-course. The innovation sought to apply principles of a practice-based approach to teacher education that was delivered in a format and could be made widely available to teachers. A multistage mixed methods action research design was conducted to examine the effectiveness of the innovation. Participants (n = 8) included elementary and middle school teachers learning to implement a new district-adopted curriculum. Data were collected to specifically consider (a) what aspects of the active learning online PD influenced learner engagement, (b) the extent to which teachers’ sense of self-efficacy changed, and (c) the effectiveness of the active learning online PD in supporting teachers’ facilitation of the district-adopted curriculum. Primary results indicated the instructional design and facilitation contributed to high levels of sustained learner engagement throughout the PD. The innovation yielded statistically significant changes in teachers’ sense of self-efficacy with implementing a district-adopted curriculum and all participants demonstrated an ability to transfer some knowledge and skills from the PD short-course into new classroom practices. Different levels of implementation of new skills were observed relative to participants degree of collective participation. Implications for practice suggest value in using Desimone’s (2009) conceptual framework as guide for designing PD to include active learning, collective participation, sustained duration, a content focus, and coherence with local context. Best practices for the design and facilitation of asynchronous online PD are discussed including learner agency, flexible pacing, frequent practice with authentic tasks, consistent feedback, and a present facilitator. More research is recommended to investigate the positive influence of a facilitator in asynchronous online PD. Additionally, research into the impact of collective participation in asynchronous online PD is recommended, with examination of ways to structure face-to-face collaboration outside of the online learning space.