We explore the structure of epistemological beliefs and its relation with the spontaneous formation of study groups in a sample of biomedical engineering students. The sophistication of the beliefs as well as the size and distribution of spontaneous small groups were measured for subjects in three different academic years: junior, intermediate and senior. Through principal components analysis, a four-factor structure was found for the epistemological beliefs, additionally validated with confirmatory factor analysis. The spontaneous small groups were determined by a clustering algorithm with data from a survey applied to 151 participants. Using parametric and non-parametric methods, it was found that the size of the group for junior students was positively correlated to naive beliefs about the source of knowledge. For senior students, however, both size and number of groups were inversely correlated to the passiveness in learning. These results are discussed in the frame of the interplay between group praxis and mental representations in the learning process. In addition, general differences were encountered between learners in spontaneous small groups and lone learners concerning the belief about the speed of learning, which also showed an overall difference across gender.