This article presents findings from an empirical study on the relations between the variables comprising learning mechanisms in small collaborative groups. Variables comprising the central learning mechanisms component were task related interactions, knowledge elaborations, and subjective estimation of knowledge acquisition. Student related determinants of the learning processes were dysfunctional behavior, and work group management. Tutor related determinants were tutor facilitative behavior (facilitation, questioning, and mini-lecturing), and tutor work group management. The selected variables were structured into a path model. The first question concerned the way the three variables comprising the learning mechanisms component are related to each other. We have contrasted mediation vs. addition hypothesis. The second question concerned the validity of the complete small group functioning model. In order to answer these questions we have constructed a questionnaire and administered it to 89 1st year medical students. Concerning the first question, the data were in accordance with the mediation hypothesis. Specific analyses showed that only the collaborative sequence type of task related interactions had positive effects on both knowledge elaborations and knowledge acquisition. In contrast the transfer of knowledge type of interactions had negative effects on the same variables. Test of the validity of the complete model showed a satisfactory model fit. Briefly, our findings suggest that a large proportion of collaborative sequences in the group, together with a low proportion of dysfunctional behavior and highly facilitative behavior of the tutor will lead to a high proportion of knowledge elaborations. Knowledge elaborations positively affect knowledge acquisition which is an important determinant of the student satisfaction and motivation.