Implementation science research points to the importance of improving implementation fidelity to improve outcomes and sustainability of interventions. Despite our growing understanding of factors related to implementation in K-12 settings, much less is known about factors influencing implementation in early childhood education contexts. Understanding factors related to how well early childhood educators implement an intervention is critical to developing ways to improve implementation fidelity and ultimately education quality. The current study explored how teacher beliefs and experiences were related to initial uptake and later implementation in a sample of 87 early childhood educators implementing a novel comprehensive curriculum, "STREAMin[superscript 3]." Across teacher dosage, classroom dosage, and teacher responsiveness, teachers with more positive initial perceptions of the curriculum had higher implementation. Teacher stress and perception of center climate were inconsistently related to implementation. Public preschool teachers and teachers with fewer years of teaching experience also reported higher levels of implementation. Implications for supporting teachers to improve implementation fidelity are discussed.