Preschool classrooms provide a unique context for supporting the development of children with social-communication challenges. This study is an uncontrolled clinical trial of an adapted professional development intervention for preschool teachers (Social Emotional Engagement-Knowledge & Skills-Early Childhood). Social Emotional Engagement-Knowledge & Skills-Early Childhood is a low-resource-intensive, transdiagnostic intervention to address the learning needs of children with social-communication challenges and consists of four asynchronous online modules and three synchronous coaching sessions. The current research evaluated the feasibility and acceptability of intervention and research procedures, implemented in authentic early childhood education settings. Participants included one teacher and one target child with social-communication challenges from 25 preschool classrooms, sampled to maximize variability. Overall, the current research revealed high levels of feasibility, with 9 out of 10 benchmarks met: (a) procedures for participant recruitment reliably identified a neurodiverse sample of children with teacher-reported social-communication challenges; (b) teachers showed high levels of program engagement and Social Emotional Engagement-Knowledge & Skills-Early Childhood completion (76%); and (c) results revealed a robust pattern of gains in Social Emotional Engagement-Knowledge & Skills-Early Childhood classrooms and associations among key outcome measures (including active engagement, student teacher relationship, social-communication competencies). Implications for the design of a subsequent, larger effectiveness-implementation hybrid trial (Type 1) are discussed.