With a continuing disconnect between structural changes to the work of teaching and the work of teachers engaged with students in classrooms, this paper addresses a growing need to attend to the way teacher professional development (TPD) is enacted in today's schools. Specifically, drawing from theories of teacher learning and numerous models of TPD that have been implemented over the past 30 years, we argue that the physical presence of students is the missing variable in the majority of TPD efforts. To help organize and advance the latest in TPD research and practice, the purpose of this article is to provide a framework for administrators, teacher leaders, and teachers to either evaluate or initiate TPD in relation to levels of physical student presence. Ultimately, we argue that changes in TPD structures cannot be expected to yield changes in TPD culture. Likewise, changes in the culture surrounding TPD cannot be expected to lead to changes in TPD structures. Rather, changes in TPD structures and culture must occur simultaneously--and students' physical presence is a potential organizing link between the two. Further, this notion is advanced through well-tested theories of learning inside and outside of Education.