This research used a mixed method research design to investigate online participation on discussion tasks by students. The research also explored the relationship between online participation and academic performance, and the teacher's role in designing the tasks and providing support for students. Ninety-five paramedic students were participants in this study. They were enrolled in a course that was delivered through the TopClass system in 2000. The research observed message posting by students and teachers' support of discussion for five subjects. Students' expectations of online participation in discussion and perceptions of studying online were collected through questionnaires and telephone interviews. These data were compared with the actual number and nature of the messages posted. Teachers' perceptions of students' engagement in online discussion were gained through interviews. The study found that student message posting in online learning situations is likely to be related to the cognitive demand and accessibility of discussion tasks that staff design and to the quality of teacher facilitation of discussion. These factors are likely to influence students' willingness to participate in online discussion and to encourage interaction with peers, although situational and personal differences between students are also factors affecting participation. Online message posting is perceived by staff and students to contribute to knowledge building among students and may be associated with improved academic performance. Further research conceming the engagement of students in online discussion is needed.