Adults are currently working alongside classteachers because of increased paren-tal involvement in schools and the integration of children with special needs. Although these new teams are likely to experience difficulties, they have formed the subject of minimal research. Teamwork research indicates that teams have difficulty in reconciling differences among members and that role definition is often problematic. Accounts of already-existing classroom teams confirm that such tensions exist. However, there are indications that by defining precisely the roles of participants, the team is made more effective. The nature of the new teams is documented through a regional survey which also gives clues to team tensions. A model is advanced on the basis of attribution theory to account for these tensions and this is tested and validated against the results of in-depth interviews with team participants. Classroom teams prove to possess little structure with minimal role definition. Team members erect defences against the tensions arising out of these loosely-structured teams; these take the form of 'status' or 'definitional' solutions to the problems participants confront. These are in turn associated with particular kinds of constructs and attributions on the part of participants. Participant observation in a secondary school support department confirms this dichotomy and indicates that in the absence of role definition, role-making evolves from interactions between participants; a model is advanced to account for and predict the nature of such interactions. The importance of clarity of role definition having been indicated throughout the research, the final element confirms experimentally an hypothesis that improving such definition will result in improved team effectiveness. Conclusions relate to the complexity and differentiation of dynamic within both homogeneous and heterogeneous classroom teams; operational strategies relat-ed to these conclusions are advanced.