This study explores teachers' experiences with School-Wide Positive Behaviour Interventions and Support (SWPBIS) at three special education (SPED) schools type 4 in the Netherlands. These SPED schools focus on supporting children with mental health difficulties or challenging behaviour. In 2014, an Act was introduced in the Netherlands with the aim of mainstreaming students with special educational needs (SEN) meaning they are educated in an inclusive environment with students who do not have such needs unless the nature and degree of those needs are such that they warrant a more specific support measure or intervention, which mainstream education cannot cater for. As a result, the manifestation of problem behaviour of students in SPED schools became more complex and intense. Based on 25 individual interviews and three group interviews with 40 SPED teachers, results indicate they experienced a safer and predictable school climate due to SWPBIS. In addition, teachers mentioned positive developments concerning team building, staff turnover and coping with a changing student population. More specifically they mentioned more open and positive communication, a sense of belonging and loyalty to their colleagues, and a shared commitment to their students in comparison to the situation prior to the introduction of SWPBIS. Staff also emphasised this approach contributed to a shared language. The development and dialogue on shared school values and the teaching of behavioural expectations as rules and procedures across school settings supported new staff-members to more easily integrate this with organisational routine and school culture and this contributed to a more predictable and safer environment for their vulnerable students.