PBL can refer to two different, but similar, teaching techniques, Problem Based Learning and Project Based Learning. There is another related technique called Case Based Learning, or CBL.
Problem Based Learning
Problem Based Learning is a technique in which students are presented with authentic and real world problems to solve. In order to make the learning authentic, students are not taught the skills needed to solve the problem directly, but instead can receive guidance from their teacher, or ask their teacher to teach them specific required skills. The teacher will not, however, provide ‘the answer’. Authentic real world problems will, in any case, be open and not have a single correct answer, but many possible solutions.
Some more information on Problem Based Learning can be found at the UQ Education Faculty Website.
Project Based Learning
Project Based Learning is similar, except that students respond to an engaging question or challenge, rather than a problem. The distinction between the two is fairly small. An excellent example of Project Based Learning at a tertiary level is the Engineers Without Borders Challenge for first year engineering students. Each year, EWB Challenge provides students with information about a specific third world or marginalised community, and challenges students to use their skills and knowledge to design a simple and culturally appropriate improvement for the community in one of several areas, such as sanitation, communication, energy or transportation.
The Buck Institute of Education provides a range of resources to assist with the implementation of PBL.
Case Based Learning
Case Based Learning is much more structured, in that the teacher provides the information needed to solve each problem at the start of each case. The teacher is also more active in guiding the students towards a preferred outcome. CBL is used in cases where there is more likely to be a correct answer, rather than for open ended questions and challenges. It is commonly used at a tertiary level in the teaching of medicine.
This reference compares CBL and PBL, in the context of medical education. It is, however, equally relevant to primary and secondary education.