Again from Barrows.
Is Problem-Based Learning Worth the Trouble? (subheading in the article)
Interestingly, this question is usually raised by people who are asked to consider the possibility of a problem based curriculum without having ever been involved in, or observing problem based learning. Once anyone is involved as a PBL tutor and has the opportunity of seeing what students can do when given permission to think and learn on their own, he or she usually becomes a convert. Faculty members can see how students think, what they know and how they are learning. This allows teachers to intervene early with students having trouble before it becomes a more difficult issue. Faculty members work with alert, motivated, turned-on minds in a collegial manner that has no equal. This is quite different from lecturing to a passive and often bored array of students whose understanding of the subject the teacher can only deduce indirectly from their answers to test questions."