The demands of good instructional design increase as the expansion of net-based education continue. In staff development at Malmö University we pay special attention to collaborative learning models. A key issue for successful accomplishment of a course is assessment and formal examination. This must reflect the instructional design of the course. Prof. Anders Nattestad, Copenhagen University and prof. Rolf Attström, Malmö University, have created a tool for examination in a virtual environment, Learning On-line , LEO, http://tmk.odont.ku.dk/leo/ . The tool is developed for educations in odontology. The tool presents a problem, which can be an authentic case. The students return their solutions into the system, which automatically presents solutions produced by ?experts?. By comparing their own solutions with the expert solutions, identify pros and cons, differences and similarities, the students analyse and evaluate their own learning. Assessment can then be based on the analysis alone or in combination with the original solutions. Studies are performed to evaluate the impact of using LEO on students´ learning, both in Odontology (Attström and Nattestad pers comm.), Teacher Education (Lundgren) and Environmental Ethics (Lundgren and Westerberg pers comm.) A further development of the tool to fascilitate collaborative work is suggested.