Early Childhood Special Education teachers select practices to use to promote social communication development for their students with autism spectrum disorder. Understanding what evidence-based practices teachers select and why can inform the development of dissemination and implementation supports at the critical Adoption-Decision stage of implementation. The researchers used discrete choice analysis to examine and test the effects of Early Childhood Special Education teachers’ beliefs (self-efficacy, attitude, subjective norms; Theory of Planned Behavior) about key evidence-based practices on their practice selections. To assess malleable determinants of practice selection, this study addressed these aims: (1) assess Early Childhood Special Education teachers’ beliefs (attitudes, subjective norms, and self-efficacy) about key evidence-based practices, (2) describe which evidence-based practices teachers selected, and (3) examine whether teachers’ beliefs predicted practice selections. A web-based survey gathered responses from 222 Early Childhood Special Education teachers. Participants had the most favorable beliefs about naturalistic intervention and the least about discrete trial teaching and scripting. These beliefs aligned with the frequencies with which these practices were selected, and teachers’ beliefs predicted which practices they selected. Together, these findings suggest that beliefs serve as determinants of Early Childhood Special Education teachers’ practice selections that can be acted on to tailor pre-implementation supports and improve implementation from the start. (author abstract)