The Level 2 Learning Programmes (L2LPs) aim to provide a broad, balanced, relevant, and meaningful education for junior cycle students with General Learning Disabilities (GLD) in the low-mild to high-moderate range of ability. In mainstream post-primary schools, it is envisioned that the majority of L2LPs’ learning outcomes can be included in mainstream subject lessons thus promoting the inclusion of students with GLD. For the effective enactment of L2LPs in mainstream classrooms teachers require continuous professional development (CPD). Research indicates that the current system of transmissive CPD in Ireland, particularly the cascading model used for L2LPs has little effect on enactment of policy initiatives, inclusive or otherwise. This study was concerned with exploring the impact of a collaborative whole-school CPD programme for the enactment of L2LPs in a mainstream post-primary school. Considerations for the CPD model included: contextual factors, relevance to job performance and student outcomes, active participation, meaningful collaboration, continuity and building capacity. The research took a predominantly case-study approach beginning with an illuminative evaluation of the school’s prior engagement with L2LPs to establish a baseline from which to develop the CPD programme. The research focused on teacher CPD; however, an important aspect was the voice of students, parents and Special Needs Assistants (SNAs) when determining the effectiveness of the CPD. The methods of data collection included pre and post-intervention attitudinal scales, interviews, participant observations and document analysis. The findings evidence improved teacher engagement with L2LPs resulting in enhanced student outcomes. The CPD had a positive impact on teachers’ knowledge, practice and beliefs, and inclusive education practices in general. There was evidence of increased collaboration and the development of a whole-school approach to L2LPs. Furthermore, there was evidence of improved student-teacher relationships as the CPD progressed. This research can be used to inform structures to support L2LPs enactment at school and national level. Recommendations are made for CPD design, L2LPs messaging and the inclusion of students,parents and SNAs in the L2LPs planning and review process.