Physics is perceived by many students to be a difficult subject, and misconceptions about it are quite common not only among school students but also among undergraduates and pre-service postgraduate science teachers. In teaching the topic of gas pressure to primary student teachers studying in the Bachelor of Education programme at my institute, I adopted a constructivist approach to guide students to resolve a problem task that was adapted from an 'egg-in-the-bottle' demonstration. The students were highly motivated to accomplish the task, and there was evidence that they were constructing or reconstructing concepts about gas pressure and applying these concepts to solve the problem, although misconceptions still abounded. It is recommended that this type of approach be utilized by secondary school physics teachers to engage students in constructing concepts and to elicit and clarify their misconceptions about other physics topics. Copyright © 2007 IOP Publishing Ltd.