Computer networks and distributed systems are characterized by highly dynamic, concurrent and complex processes. Thus, training in this area requires great effort from both teachers and learners. Teachers are unsatisfied with available methods for presentation, explanation and exercises. They are looking for more adequate ones to better support learners. We have developed an architecture called HiSAP (Highly interactive Simulation of Algorithms and Protocols). It consists of a framework to build simulations and generate applets from formally specified algorithms or protocols. By modifying this specification and observing the resulting behavior, teaching and learning in a constructive manner is enabled. The framework is open to plug-in tools to show different aspects of this behavior. We present results of some experiments concerning the usage of HiSAP during three different lectures about distributed systems and computer networks for graduate students.