The emphasis on social-emotional competence and its importance to positive academic and nonacademic outcomes has led to a focus on identifying and implementing effective practices for supporting young children's social-emotional competence. Our work to identify, validate, and support the fidelity of implementation of evidence-based practices to promote young children's social-emotional competence and to address challenging behavior has focused on the Pyramid Model for Promoting Social-Emotional Competence in Infants and Young Children framework (Fox et al. in Infants Young Child 23:3-14, 2010; Hemmeter et al. in Sch Psychol Rev 35:583-601, 2006; Hemmeter et al., in: Buysse, Peisner-Feinberg (eds) Handbook of response-to-intervention in early childhood, Brookes, Baltimore, 2013). The implementation of the Pyramid Model practices to provide effective intervention that leads to meaningful child outcomes will require that practitioners are able to implement the practices with fidelity. Implementation science provides guidance on the "drivers" or key components that must be in place within a system to ensure the use of evidence-practices or interventions (Blase et al. in stages of implementation analysis: where are we? FPG Child Development Institute, University of North Carolina, Chapel Hill, 2013; Metz et al. in an integrated stage-based framework for implementation of early childhood programs and systems. OPRE Research Brief OPRE 201548, 2015). In this paper, we address competency drivers by describing an instrument that has been developed, validated, and used to measure the fidelity with which practitioners implement Pyramid Model practices. In addition, we describe the professional development intervention we have used to support teachers to implement the practices with fidelity. We focus on how a fidelity tool can be used to measure practice implementation as well as to guide professional development focused on the practices. [This article is published in "School Mental Health" (EJ1229476).]