Schools play a major role in delivering behavioral health services to autistic youth. School culture and climate are strong predictors of the extent to which these services incorporate evidence-based practices; however, little is known about how school leaders shape culture and climate. Drawing on the concept of culture and climate embedding mechanisms, we conducted a qualitative study to understand the ways in which school principals embed cultures and climates that support effective implementation of evidence-based practices for youth with autism. Semi-structured interviews with 32 teachers in schools that implemented three closely related evidence-based practices for youth with autism (discrete trial training, pivotal response training, and visual schedules) explored teachers' experiences regarding (a) implementation of the three evidence-based practices, (b) perceptions of school culture and climate, and (c) principals' behaviors, practices, and decisions that supported or detracted from the aspects of culture and climate that supported successful implementation. Thematic analysis detailed seven mechanisms that principals used to embed cultures and climates that shaped evidence-based practice implementation. These mechanisms represent actionable targets for school leaders and inform strategies to improve the implementation of evidence-based practices for youth with autism in schools.