The integration of collaborative technologies with simulation provides new opportunities to assist the learners in a more interactive, active, motivating, and productive way and at the same time facilitates confronting more complex problems. This integration has been put into practice in a collaborative environment for the teaching and learning of house automation. Teachers use this environment to configure collaborative learning activities based on problem solving. Then, students, working at the same time but from different locations, collaborate in building models as solutions to the problems and in evaluating the models through the use of simulation. This article describes this environment and its collaborative simulation tool, called COSTHA. It focuses on the object-oriented modeling of the domain, on the formalization of the problems to solve, on the features of COSTHA as a collaborative simulator, and on its architecture and implementation.