This project explored changes in adolescents’ delinquency across the high school years, and key developmental features that might condition youths’ involvement. Namely, in an effort to inform treatment and prevention, we focused on the (potentially modifiable) roles of perceived rewards of antisocial behaviour, self-control, and emotions in driving delinquency, over years and over days. To do so, we leveraged two rich data sets with a focus on socio-economically disadvantaged Australian youth. Project findings pointed to a robust association between high reward sensitivity and high levels of delinquency. Moreover, findings suggested that up-ticks in delinquency over the high-school years led to subsequent increases in reward perceptions. Yet these relations differed based on youths’ self-control. Low self-control coupled with high perceived antisocial rewards characterized youth at-risk for very high delinquency involvement. In addition to antisocial rewards, findings highlighted emotional inflexibility as a risk factor. Youth with a strong reward bias engaged in antisocial behaviour, regardless of their emotions; whereas youth with low reward bias were “swayed against” antisocial choices when especially worried. They were also more likely to engage in antisocial behaviour when particularly bored. Notably, we explored findings with an advisory panel of law enforcement personnel, who assisted with practical interpretations of results.