A first major challenge is to develop procedures that help us to combine and integrate the World of Knowledge and the World of Work in teaching. One approach may be to take competencies as a starting point, and analyze these competencies in order to develop task classes (also called "case types", van Merriënboer, 1997) that give an abstract, general description of a broad category of learning tasks. On the one hand, such task classes allow one to identify the knowledge that may be helpful in solving a particular category of problems in the domain of study. It allows for the teaching of larger, integrated bodies of knowledge, as we used to do in the World of Knowledge. On the other hand, task classes might also be used for helping content experts to identify professional tasks that are really useful as learning tasks − and so bring in the World of Work. Each learning task should nicely fit the task class it exemplifies, and the complete set of learning tasks for a particular task class should provide a good mapping of all the skills and knowledge required for solving the problems in this class. This approach has been successful in training for complex skills (see Clark & Estes, 1999).