Classroom teachers and occupational therapists need to work together if they are to meet the needs of learners with profound intellectual and multiple disabilities (PIMD), but how they navigate their multi-agency working in this area of practice is largely unknown. Guided by the conceptual framework of activity theory, where learning is recognised as being an intrinsic part of activity, this study has a specific focus on the multi-agency practice of classroom teachers and occupational therapists as they work and learn across professional boundaries and provides an understanding of the factors that have influenced their activity systems and interactive relationships as well as interpretations of their own, and each other’s professional identities, roles and responsibilities in this specialist field of work. A qualitative research design was used and included individual interviews and focus groups. The data gathered reflected the multi-layered nature of multi-agency practice in complex situations. The occupational therapy and classroom teacher participants were able to analyse and consider their everyday activities and how these supported or constrained their ability to work collaboratively towards joint goals and outcomes. This process aided expansive learning through an adapted change laboratory approach and boundary crossing learning mechanisms to allow for discussion and ideas to emerge for future enhanced ways of working which could impact on future practice. The suggestions made during this research were in two key areas: firstly in the professional roles and identity of the classroom teacher and occupational therapy participants in their roles and ways of working to meet the needs of learners with PIMD and secondly, in relation to the supports and constraints they experienced in their multi-agency working and learning as they carried out their roles. This study enriches the literature on the multi-agency practice of classroom teachers and occupational therapists working with learners with PIMD and also makes a methodological contribution in its use of elements of activity theory and boundary crossing to link the beliefs and ways of working of the participants to provide a more comprehensive understanding of their multi-agency working and learning.