In many countries, teaching assistants are working in schools in increasing numbers. While they formerly supported teachers by completing low-level administrative tasks, they are increasingly playing a pedagogical role and working directly with pupils, particularly those with special educational needs. However, little is known about the quality of the support that teaching assistants provide to these pupils. This paper systematically examines differences in the types and quality of interactions teaching assistants have with pupils compared with the interactions of teachers in the same classrooms. Differences were found, particularly in relation to the development of pupil thinking, and examples of the differential interactions are provided in the paper. Recommendations are made related to the need to examine existing models of teaching effectiveness to take account of the role of teaching assistants in classrooms and the role of teachers managing teaching assistants. (Contains 1 table and 1 note.)