What effects does PBL have on student learning outcomes, knowledge acquisition, and higher order thinking skills? This question continues to influence the adoption and implementation of problem-based learning (PBL) since its inception. The answer to this overarching question is still lacking. This chapter responds to this question by first analyzing and synthesizing the literature regarding the factors that influence the effectiveness of PBL to identify questions that designers and researchers should ask about results of learning. It then explores important characteristics of PBL compared with its analogous pedagogies and approaches of project-based learning, case-based reasoning, inquiry-based learning, learning design and/or design thinking in an effort to understand how features of each approach influence the effectiveness of learning outcomes. Further, the chapter examines how PBL approaches and pedagogies define learning outcomes and how various learning outcomes are measured. Finally, the chapter offers a synthesis of research on the effectiveness of PBL and recommendations for the future researchers and designers. [For the complete proceedings, see ED600498.]