In this chapter we explore the ways in which researchers can work collaboratively with schools to develop complex interventions designed to improve public health. We begin by summarising the importance of young people’s health as a focus for this work, and the importance of schools as a setting for health improvement. We then turn our attention to the increasing emphasis now being placed on working collaboratively with schools to co-produce new health improvement interventions. Drawing on Wight et al.’s (2016) framework for intervention development – 6SQUID – we consider how this co-production can contribute to intervention development at four critical stages: defining the problem to be addressed by the intervention; which aspects of the problem are most amenable to change; defining and describing the change mechanisms that will achieve the intervention’s key goals; and the formulation of implementation systems and strategies. We also examine how members of a school community can be involved in shaping the aims, design and conduct of evaluation studies that accompany intervention development. The final part of the chapter reflects on some of the key challenges that researchers face when seeking to co-produce interventions and possible strategies for overcoming these.