This mixed methods dissertation study explored how secondary school educators in specific K-12 competition programs recruited and deployed STEM professional volunteers. The study explored which practices were viewed as most important, and how practices related to constructivist pedagogy, all from the viewpoint of educators. The non-positivist approach sought new knowledge without pursuing generalized results. Review of the literature uncovered extensive anecdotal information about current practices, and suggested that large investments are made in engaging volunteers. One National Science Foundation-sponsored study was identified, and its recommendations for a sustained research agenda were advanced. Three study phases were performed, one to explore practices and operationalize definitions, a second to rate practice's importance and their relation to pedagogy, and a third to seek explanations. Educators preferred recruiting local, meaning recruiting parents and former students, versus from industry or other employers. Most educators preferred volunteers with mentoring skills, and placing them in direct contact with students, versus deploying volunteers to help with behind-the-scenes tasks supporting the educator. Relationships were identified between the highest-rated practices and constructivism in programs. In STEM professional volunteers, educators see affordances, in the same way a classroom tool opens affordances. A model is proposed which shows educators considering practicality, pedagogy, knowledge and skills, and rapport when accessing the affordances opened by STEM professional volunteers. Benefits are maximized when programs align with strong industry clusters in the community.