The National Science Foundation (NSF) holds a primary responsibility for overseeing the federal government's efforts to foster the creation of a STEM-capable workforce. As part of its efforts in this endeavor, NSF's Directorate on Education and Human Resources asked the National Academies of Sciences, Engineering, and Medicine to convene a workshop that would contribute to NSF's preparation of a theoretical and evidence-based STEM Workforce Development R&D Core Framework. Participants discussed research themes, identified gaps and emerging research opportunities, and recommended refinements in the goals of the framework. This report summarizes the presentations and discussions from the workshop.