Most courses via Internet use the electronic forum, which allows for cognitive dialogue, namely through critical thinking. The tutor’s support to collaboration, reflection and learning can explore the characteristics of e-forums and contribute to a more positive academic experience. This study aims to identify which of the tutor’s tasks are more influential on higher levels of collaborative critical thinking, with a content analysis of 5200 messages in several on-line Master’s and Post-graduation courses forum. 11 indicators of the tutor’s intervention and four indicators of collaborative critical thing were adopted. Then, a Cramer’s V post-test was used to assess the effect of the tutor’s posts on the highest levels of collaborative critical thinking. The tutor’s tasks which relate more to the students’ highest levels of critical thing were: 1) asking open questions to the students, 2) establishing associations among the students’ messages and 3) modelling the debate. The study provided useful information on the ways of triggering the dialogue and taking it to higher cognitive levels
