Given the size of the investment in professional development for early childhood educators and the dependence of educational reform on providing high quality professional development, the knowledge base of effective practices needs to be strengthened. In this paper, the authors report on the results of an effort to better understand the independent contribution of coaching as the sole mechanism for improving teacher practice and child outcomes in early language and literacy development. They compare coaching with traditional training through coursework, and a wait-list comparison group. The results they report here build on a previous large-scale analysis of professional development for center- and home based providers. Together, the earlier study and the one reported here help to highlight the strengths and potential weaknesses of different forms of professional development for improving teaching practices in early literacy. In addition, it provided some initial insights on the issue of dosage and intensity of professional development outside of our ability to directly subject it to experimental manipulation. The goal of the study was to examine the effects of coaching or professional development coursework on teacher knowledge and teacher practice. Center-based child care teachers were randomly assigned to receive either coaching or professional development coursework, with a wait-list comparison group who received no professional development serving as controls (e.g. business as usual). (Contains 3 tables.)