This paper starts from the assumption that leaming is promoted through confronting students with the inconsistencies entailed by their own beliefs. The issue is explored in the domain of Newtonian dynamics in the context of one or more moving particles. Previous work is used as the basis for the construction of a programme of work that is undertaken by a group of students. This programme entailed the development of a computer-based modelling environment called DYNLAB. The underlying design principle is that students should be able to model the agencies involved at a level which permits them to express some of their explicit (possibly mistaken) beliefs about relevant concepts. Other, implicit, beliefs should also be detectable through use of the system. The results derived from observation suggest that computer-based modelling facilities can provide advantages over approaches exploiting other media. In particular, such systems can be used to promote the kinds of intellectual conflict that are believed to be beneficial.