Structural, process, and content dimensions of a coaching-based professional development (PD) intervention were examined in an implementation fidelity study. The intervention focused on Head Start teachers' vocabulary and phonemic awareness instruction, and was delivered through onsite classroom visits and technologically mediated methods that included a video-intensive hypermedia resource. There was a high level of compliance with the intended number of coaching sessions and with the amount and focus of coach feedback on teachers' observed practices. Teachers' independent viewing of practice exemplar videos was highly variable. Onsite coaching sessions compared with technologically mediated coaching provided more feedback on practices that extend learning objectives beyond whole group time and that focus on learning goals of individual children. Coach feedback in onsite sessions also included more specific items offered for the first time, whereas technologically mediated feedback included more items that were repeats or expansions of feedback provided in a prior session. Implications for the design of coaching programs and future research on active ingredients of coaching are discussed. (author abstract)