This study investigated how adult education teachers changed after participating in one of three different models of professional development (multisession workshop, mentor teacher group, or practitioner research group), all on the same topic of learner persistence. The study also investigated the most important individual, professional development, program, and system factors that influenced the type and amount of teacher change. This study was conducted primarily to help professional development decision-makers plan and deliver effective professional development, and to understand the factors that influence how teachers change as a result of professional development. Overall, teachers who gained the most from participating in professional development were those who: worked more hours in adult education, had well-supported jobs (good benefits, ample prep time, paid professional development release time), had a voice in decision-making in their programs, had their first teaching experience in adult education, were relatively new to the field, had more access to colleagues, did not have an advanced degree (above Bachelor's), and participated for more hours in high-quality professional development. [For the full report, see ED508607.]