Interactive exercising is one of the major ingredients of technology-enhanced learning. It reaches its full potential only, when appropriate feedback is given to the learner. This paper describes a principled approach for representing and processing interactive exercises in ActiveMath. This approach relies (1) on a modular architecture of the exercise player, (2) on a separation of different types of knowledge that have to be handled to generate feedback, and (3) on a generic representation of interactive exercises. The paper describes how all this works together in LeActiveMath
