Factors associated with Head Start staff participation in a classroom-based professional development project to promote their use of evidence-based child learning opportunity practices and evidence-based responsive teaching procedures were examined in a study of 36 teachers and teacher assistants in 19 different classrooms. The factors constituting the focus of investigation included work climate, staff belief appraisals (career aspirations, personal motivation, Developmentally Appropriate Practices beliefs), staff receptiveness to the professional development training, staff judgments of the social validity of the practices constituting the focus of training, and staff background characteristics (age, education, years of experience). Results showed that Head Start staff members' personal beliefs, receptiveness to the training, and their judgments of the social validity of the classroom practices constituting the focus of training were related to staff judgments of their participation in the training which in turn were related to their active engagement in learning to use the classroom practices. The implications of the findings for practice are described in terms of the need to use methods and procedures that actively engage staff in professional development opportunities.