Peer-led team learning (PLTL) research has expanded from its roots in program evaluation of student success measures in Workshop Chemistry to a spectrum of research questions and qualitative, quantitative, and mixed methods study approaches. In order to develop recommendations for PLTL research and propose best practices for faculty who will integrate PLTL in their classrooms, the theoretical frameworks, study designs, results, and limitations of sixty-seven peer-reviewed studies, spanning a variety of STEM disciplines and institution types, were examined. Five program evaluation themes emerged from this synthesis of the literature: student success measures; student perceptions; reasoning and critical thinking skills; research on peer leaders; and variants of the PLTL model. For each of the themes, areas for future study and implications for practice are suggested to STEM discipline-based education researchers and faculty.