The paper explores how youth engagement (i.e. organised social participation in a group, club, or activity) can impact young people's interethnic attitudes, via pathways of positive and negative interethnic contact. To do so, it examines processes of interethnic cohesion occurring on a large-scale, nationallyimplemented UK youth engagement scheme. Employing a quasiexperimental approach, using pre-test/post-test data on a sample of participants and a (propensity-score matched) control-group, analyses demonstrate that participation leads to positive changes in young people's interethnic attitudes, evident at least 4-6 months after participation ended. This improvement in attitudes is driven primarily by increases in young people's positive interethnic contact, while participation has no impact on young people's levels of negative interethnic contact. However, the impact of participation on interethnic attitudes depends on how much positive contact young people had prior to taking part: young people who joined the scheme with less frequent positive contact see substantially larger improvements in their levels of positive contact which, in turn, drives even greater improvements in their interethnic attitudes. These findings provide encouraging evidence that sites of youth engagement, especially national engagement schemes, can foster intergroup cohesion among adolescents; especially among those with less frequent positive contact in their daily lives.