Our papers explore how interventions (e.g., peer-led programmes in schools) effect change not purely by delivering content, but by interacting with peer-networks and shifting perceived norms. For example, analyses examine how students with high centrality or high norm-sensitivity may serve as conduits of change, or conversely how weaker network ties may hamper diffusion. While each paper addresses different contexts (smoking prevention, physical-activity norms, etc), a recurring finding is that the mechanism of change is often relational: network-embedded students adapt more when the intervention activates norm-signals through their peer ties.