The Intelligent Tutoring System (ITS) uses the Internet as a constructivist learning environment and aims to provide intelligent assistance to improve both quality of training and distribution of knowledge in a distance learning situation. The assistance is based on various intelligent Agents which act collaboratively to support learning at different steps. A first Agent (pedagogical Agent), close to the learner, is able to detect his difficulties using a learner model and provides local explanations when needed or on request. A second Agent (dialog Agent) provides access to other explanations or learners available on the Web, in synchronous or asynchronous mode. Taking into consideration all possible helps a third Agent (negotiating Agent) is in charge of finding and selling explanations according to a market of requests and helps. A fourth Agent (moderator) in charge of determining which explanation was finally useful to serve as a permanent source of explanation for future learners