What’s a PBL flipped classroom?. It’s really about flipping the emphasis of time. In a PBL flipped scenario, the teacher mainly works before the project begins (rather than lesson) and not after. They do work during, but unlike even a video-flip, the teacher isn’t doing the bulk of the work (marking) at the end. The end is a celebration and feedback time. Almost all the assessment will have been handled during the project.