The development of instructional technology increases the use of synchronous e-learning procedures which enable real-time interactions. The study explores whether the willingness to participate as well as actual participation in synchronous group discussions is affected by participant personality (extroversion-introversion), medium characteristics and discussion topic sensitivity. The research is composed of two sequenced sub-studies. The first one investigates the willingness to participate while the second study explores the degree of actual participation in discussions. An online self-report questionnaire was completed by 405 adult Internet users. Following that, 120 volunteers extracted from this sample were randomly assigned to face-to-face, audio conferencing, or textual chat gender-mixed experimental conditions and conducted two short discussions (having low and high degrees of topic sensitivity). The relation between estimated and actual participation was explored, as well as the equalization effect of online interactions. The first study findings show that, in general, participants prefer conventional over sensitive discussion topic; they also prefer face-to-face discussion rather than online communication. As hypothesized, participant personality affects the willingness to partake in discussions: extroverts prefer taking part via a more revealing communication medium; introverts express greater readiness for discussion via textual chat. The results of the study expand the understanding of student behaviour in synchronous e-learning.