The concept of project-based learning (PBL) has garnered wide support among a number of K-12 education policy advocates and funders. This working paper builds on and updates a seminal literature review of PBL published in 2000. Focused primarily on articles and studies that have emerged in the 17 years since then, the working paper discusses the principles that underlie PBL, how PBL has been used in K-12 settings, the challenges teachers have confronted in implementing it, how school and district factors influence its adoption, and what is known about its effectiveness in improving students’ learning outcomes.

PBL is grounded in cross-cutting “design principles” often related to what is taught, how it is taught, and how students should be evaluated in a PBL classroom. PBL design principles emphasize the importance of the project as the central vehicle of instruction and of students as active participants in the construction of knowledge. There is little consensus among developers of PBL design principles, however, about how PBL fits in with other instructional methods, how long a PBL unit should last, the roles of student choice and collaborative learning, and how learning should be assessed. The lack of a uniform vision complicates efforts to determine whether PBL is being implemented with fidelity and to evaluate its effects.

PBL can be introduced into classrooms in a number of ways: Teachers and schools can make use of externally developed PBL curricula, they can develop their own PBL approaches, or PBL can be part of a whole-school reform effort. Implementing PBL is often challenging. It requires that teachers modify their roles (from directors to facilitators of learning) and that they tolerate not only ambiguity but also more noise and movement in the classroom. Teachers must adopt new classroom management skills and learn how best to support their students in learning, using technology when appropriate. And they must believe that their students are fully capable of learning through this approach. Given these challenges, professional development — both initial training and continuing support — is likely to be essential to the successful implementation of PBL.

The working paper suggests that the evidence for PBL’s effectiveness in improving students’ outcomes is “promising but not proven.” Evaluations of its effectiveness have been hampered by the paucity of valid, reliable, and readily usable measures of the kinds of deeper learning and interpersonal and intrapersonal competencies that PBL aims to promote. Many studies, too, have used evaluation designs that leave open the possibility that factors other than PBL were responsible for the outcomes that were found. This said, some studies have found positive effects associated with the use of PBL curricula in science and social studies classes. Evidence for its effectiveness in math and literacy classes is more limited. In particular, it has been noted that math teachers have found it difficult to integrate PBL into their instruction.

Some studies in schools that follow PBL approaches have pointed to positive effects on students’ engagement, motivation, and beliefs in their own efficacy, although the specific PBL model and the intensity of its use have varied across these schools.

The working paper concludes with recommendations for advancing research and knowledge about PBL.