This mixed-methods study examined the effects of different models of online professional development (PD) on 21 US elementary teachers’ writing instruction, on the teachers’ confidence, and on students’ writing quality. Participants were first-grade teachers who were randomly assigned to one of three conditions: Coaching-plus-Manual (C+M), Manual (M), or Business-as-Usual (BAU). All teachers received online-PD but the C+M and the M conditions received PD on genre-based writing-strategy instruction. The M group taught using only the manual of that approach but the C+M also received coaching. Results found that C+M teachers increased the most in their writing confidence, and C+M students wrote papers of better quality at posttest compared to the M and BAU students.