Socio-constructivist perspectives on adult education, as well as many practitioners in the field, assume that the teacher's interpersonal attitudes influence the process of knowledge construction on the part of the participants. The aim of this paper is to contribute to an empirical evaluation of this view, and in particular: (1) to understand whether the actions enacted by an educator towards learners may be taken as local cues of her underlying general interpersonal attitudes in and about the situation; (2) to try to describe such behaviours and to gather them into meaningful clusters; (3) to explore possible differences in the general interpersonal attitudes of novice vs. expert educators; and (4) to correlate such attitudes with the learners' behaviours. Fifteen training courses for adults, each involving different educators, participants and topics, were observed. All the courses took place in classrooms in the city of Torino, Italy. Each course was simultaneously observed by three independent judges. Factor analysis led to the identification of four main interpersonal attitudes of the educators, namely "favouring cooperation," "directivity," "flexibility," and "focusing on the group." These attitudes were then correlated to indexes of the participants' levels of attention, participation and understanding. The results corroborate the hypothesis that the interpersonal attitudes of the educators correlate with the mental attitudes of the learners. In particular, a cooperative orientation appears to foster the conditions for the construction of new knowledge. The two subgroups of expert and novice educators achieved different levels of effectiveness. Overall, our findings support the idea that learning is a process of knowledge transformation that takes place within an interpersonal context. (Contains 6 tables and 1 note.)