Novice problem solvers are rather sensitive to surface problem features, and they often resort to trial and error formula matching rather than identifying an appropriate solution approach. These observations have been interpreted to imply that novices structure their knowledge according to surface features rather than according to problem type categories. However, it may also be the case that novices do know problem types, but cannot map the problem at hand to a known type, because they fail to create a sufficiently well-elaborated problem representation. This study aims to distinguish between these explanations. In this study novice physics students at high and low levels of proficiency completed two problem-sorting tasks from the domain of electricity and magnetism, one with and one without elaboration support. Results confirm that these students do distinguish problem types in accordance with their required solution approaches, and that their problem-sorting performance improves with elaboration support. Therefore, it was concluded that their major difficulty lies in the process of matching concrete problems to a proper category. Within-group analysis revealed that the performance of proficient novices clearly improved with elaboration support, whereas the effect for less proficient novices remained inconclusive. The latter finding is explained from the less proficient novices' problem representations being too fragmented to integrate new information. These results suggest that, in order to promote schema-based problem solving, instruction in the domain of electricity and magnetism should be based not so much on restructuring the conceptual knowledge base but rather on enriching situational knowledge.