This study compared effectiveness of "business as usual" to that of 4 professional development (PD) programs that targeted teachers of at-risk preschool children. A 2 x 2 design was used to cross mentoring and progress monitoring conditions among the 4 PD programs. Specifically, some teachers received both in-classroom mentoring and detailed, instructionally linked feedback concerning children's progress in language and literacy. Some teachers received no mentoring but did receive the detailed, instructionally linked feedback concerning children's progress. Some teachers received in-classroom mentoring but only limited feedback on children's progress, which was not linked to curricular activities. Finally, some teachers received no mentoring and only limited feedback concerning children's progress. All 4 PD conditions included the same year-long, facilitated online course that emphasized language and literacy instruction, practice of learned material in one's classroom, and participation in online message boards with fellow teachers. Across 4 states, 158 schools (N = 262 classrooms) were randomly assigned to 1 of the 4 PD conditions or business as usual. The condition that included online coursework combined with mentoring and detailed, instructionally linked feedback yielded the greatest improvements in teaching behavior and children's school readiness. (Contains 2 tables and 4 figures.)