Policymakers have underscored the importance of professional development (PD) opportunities for supporting the early childhood education workforce. Yet little is known about how the scope and delivery of PD opportunities impact the extent to which the content provided informs classroom practice. In the present study, we explored how teacher fidelity of implementation differs by the PD scope and delivery, and the role it plays in overall classroom quality. Lead teachers in under-resourced preschool centers were randomly assigned to one of three PD conditions: (1) a broad-based program focused on incorporating children's cultural funds of knowledge throughout the day, delivered via an in-person coach, (2) a culturally grounded classroom storytelling program that is narrow in scope and delivered via in-person coaching, (3) a culturally grounded classroom storytelling program that is narrow in scope and delivered via an animated webinar series. Findings showed that teachers' fidelity of implementation was higher when trained in a classroom program that is narrow in scope, fidelity did not vary by mode of delivery (i.e., in-person coaching vs. webinars), and that higher fidelity of implementation was predictive of more supportive classroom practices. Results are discussed in relation to implications for best practices surrounding in-service professional development opportunities.