This study examines the impact of 2 forms of professional development on prekindergarten teachers' early language and literacy practice: coursework and coaching. Participating teachers (N = 148) from 6 urban cities were randomly assigned to Group 1 (coursework), Group 2 (on-site coaching), or Group 3 (control group). Pre- and postassessments examined teachers' knowledge and quality of language and literacy practices. Analyses revealed no significant improvements between groups on knowledge of early language and literacy. However, those who received coaching made statistically significant improvements in the structural environment both immediately and 5 months later. Effect sizes were substantial for coaching, while those who received coursework made no significant improvements. Analyses of the active ingredients of coaching were examined using logs and interviews to further elucidate these findings. Results indicated that coaching appears to be an effective form of professional development for early childhood educators.