Public speaking is a non-trivial task since it is affected by how nonverbal behaviors are expressed. Practicing to deliver the appropriate expressions is difficult while they are mostly given subconsciously. This paper presents our empirical study on the nonverbal behaviors of presenters. Such information was used as the ground truth to develop an intelligent tutoring system. The system can capture bodily characteristics of presenters via a depth camera, interpret this information in order to assess the quality of the presentation, and then give feedbacks to users. Feedbacks are delivered immediately through a virtual conference room, in which the reactions of the simulated avatars can be controlled based on the performance of presenters.