Problem-based learning is one of many approaches that attempt to move away from "sage on the stage" and content-based instruction to "guide by the side" and issue-based collaborative learning.

"Problem-Based Learning is an educational strategy that involves the presentation of significant, complex, and 'real-world' problems to students, that are structured in such a way that there is not one specific correct answer or predetermined outcome. In this approach, students work in small groups to negotiate a common understanding of the problem." (Gurrie, 2003)

Gurrie's (2003) Increasing Student Motivation and Quality of Participation in Discussions through Problem-Based Learning is a good, short introduction to the basics of the approach.