This empirical study examined teacher self-reported participation (using or not using) and engagement (posting or lurking) in the online Advanced Placement (AP) Teacher Communities (APTC) coinciding with the redesigned AP Biology, Chemistry, and Physics exams and curricula. Prior analyses indicated that APTC participation has positive, direct associations towards teacher practice and students' scores, motivating further exploration. Based on teacher self-reported data, this analysis suggested that significant differences in teacher, teaching, and school characteristics predicted whether a teacher was using or not using the APTC. However, there were not substantive differences in most characteristics between the types of engagement, such as lurking and posting. Insights about teacher learning from online peer communities in this study might generalize to other national shifts in curriculum and assessment, such as the Next Generation Science Standards or Common Core State Standards.