There is increasing international concern about the mental health and well-being of school-aged children, and the school is often seen as the optimum setting to deliver interagency interventions. This paper draws on a Scottish study examining the responses of local authorities, schools and other agencies to challenging behaviour related to poor mental health. It explores the ways in which the presence of workers from other agencies had an impact on the capacity of schools to respond to such issues. In Bourdieuan terms, the study showed that non-teaching workers imported into school developed new forms of ‘habitus’ leading to effective team work to support vulnerable pupils, but that they often operated in isolation from the wider teaching staff. Different professional cultures created significant barriers, which could be exacerbated by active resistance to meaningful engagement. Consequently, parallel working evolved, where staff from agencies other than education supported pupils experiencing difficulties, but there was little evidence of corresponding changes to ethos or pedagogy to meet the needs of pupils in school. Expertise pertaining to the mental well-being of pupils thus tended to be compartmentalized and was not readily transferred elsewhere, and this led to a disjointed experience for pupils. Our evidence strongly suggested that teachers preferred to learn from other teachers. This served to reinforce existing habitus and to isolate them from new ways of thinking. Potential ways of effecting culture change are suggested, through innovative training and development, linked to accountability, to challenge the new mode of parallel working before it becomes the status quo.