Improving teacher quality is arguably the most effective way to improve student achievement. Online professional development (OPD) has great potential to improve teacher quality. There is a dearth of scientific research, however, on whether changes in teachers' knowledge and instructional practices resulting from OPD are linked to changes in students' knowledge and practices. This paper presents the results of a randomized controlled trial exploring the effects of a learning-community model of OPD for teachers on the knowledge and practices of their students in the context of fourth grade English language arts. There were significant treatment effects for some student outcomes; the effect sizes, however, were small. (Contains 10 tables.)