This paper deals with collaborative knowledge construction in videoconferencing. The main issue is about how to predict individual learning outcome, in particular how far individual prior knowledge and the collaborative knowledge construction can influence individual learning outcomes. In this context, the influence of prior knowledge and two measures of instructional support, a collaboration script and a content scheme were analyzed concerning the collaborative knowledge construction. An empirical study was conducted with 159 University students as sample. Students learned collaboratively in groups of three in a case based learning environment in videoconferencing and were supported by the instructional support measures. Results show that collaborative knowledge construction had more impact on individual learning outcome than individual prior knowledge.