Research has demonstrated that the professional development of staff is prioritised by effective school leaders. A limited, but growing research base has noted the potential influence of middle leaders, i.e., teachers with formal leadership responsibilities, to build teachers’ professional capacity. This paper examines middle leaders’ development of others’ professional and leadership capacities. It uses a mixed methods approach, analysing qualitative interview and social network data. While the qualitative data distils several key themes, the social network analyses sheds light on the interactions that support teachers’ development. The findings examine how middle leaders facilitate teacher empowerment and team building by (a) mediating instructional initiatives, (b) devising structures for curriculum enactment, and (c) creating opportunities for professional dialogue.