Problem-based learning  (PBL) is a student-centered approach in which students learn about a subject by working in groups to solve an open-ended problem. This problem is what drives the motivation and the learning.  (
https://teaching.cornell.edu/teaching-resources/engaging-students/problem-based-learning )

The difference between PBL’s

Problem-based learning typically follow prescribed steps:

1. Presentation of an “ill-structured” (open-ended, “messy”) problem
2. Problem definition or formulation (the problem statement)
3. Generation of a “knowledge inventory” (a list of “what we know about the problem” and “what we need to know”)
4. Generation of possible solutions
5. Formulation of learning issues for self-directed and coached learning
6. Sharing of findings and solutions

If you’re a project-BL teacher, this probably looks pretty familiar, even though the process goes by different names. Other than the framing and the more formalized steps in problem-BL, there’s really not much conceptual difference between the two PBLs — it’s more a question of style and scope:

John Larmer (
https://www.edutopia.org/blog/pbl-vs-pbl-vs-xbl-john-larmer )