This study examines the impact of professional development on teacher knowledge and quality early language and literacy practices in center- and home-based care settings. Participants from 291 sites (177 centers; 114 home-based) in four cities were randomly selected to: Group 1, 3-credit course in early language and literacy; Group 2, course plus ongoing coaching; Group 3, control group. Analysis of covariance indicated no significant differences between groups on teacher knowledge. However, there were statistically significant improvements in language and literacy practices for teachers who received coursework plus coaching with substantial effect sizes for both center- and home-based providers. Professional development alone had negligible effects on improvements in quality practices. Coursework and coaching may represent a promising quality investment in early childhood. (Contains 5 tables and 1 figure.)