The move to include students with special educational needs (SEN) in mainstream education is one of the priorities of educational reform agendas in many countries. Also in Flanders (Belgium) the government's aim is to implement a more inclusive school system, but this faces some resistance from practitioners. This study examines the way in which professional development initiatives (PDIs) supporting inclusive education can reduce this resistance. PDIs are defined by nine key features, which are subdivided in four core (referring to the content): (1) content focus, (2) pedagogical knowledge, (3) coherent and evidence-based, and (4) ownership; and five structural features (referring to the design of a PDI): (1) duration, (2) collective or collaborative participation, (3) school- or site-based, (4) active learning, and (5) trainer quality. The results indicate that school team members' positive experiences with students with special educational needs (SEN) have more impact on the willingness to include them than the core or structural features of PDIs. Furthermore, indications were found that PDIs focussing on a specific SEN can create more willingness to include these students.