Synchronous on-line learning can occur constructively. In this environment it is important to allow time for small talk at the beginning of a session (and potentially during as wel, depending on how teh course is structured). This builds trust between the students and the instructor that helps to facilitate more interaction and a better learning experience. One word of caution for synchronous on-line environments: it is easy to forget that there is a group, so be careful to handle any potential criticism or ranking/grading of students' material individually. A seperate individual email or one-on-one synchronous session may be necessary for this.
