The chat is a tool as well as a service for synchronous communication on the Internet and has been raising controversy among academics. Because its interface apparently allows for intuitive use (derived from web chats), chats are believed to be easy and good to use in educational settings. To test the tool, an academic chat session was planned by students and teachers of a subject in a post-graduate program. The session was thought to have failed to meet its goals and was then taken up for study from different theoretical-methodological view points so that it was possible to account for the reasons that might have originated the sensation of failure. The study focused on interpersonal relations, difficulties to follow the rhythm of conversation, difficulties related to asymmetry among participants, difficulties due to unpredictable development of topics, phases of knowledge construction and operational difficulties. Among results derived from the analyses, it was possible to demonstrate the impact of previous experience in the educational use of chat on the development of topics, conversational rhythm and interaction. It was also possible to reveal the impact of teacher's role and previous experience on the phases of knowledge construction identified in students' conversational turns. Results suggest that successful educational chats require careful preparation so that there is little digression, topic maintenance and clear focus on discussion topics. Teacher mediation must be equally careful so that incentive is given to problem raising and synthesis besides support to inexperienced students so that they have their share in the contribution with new information.