Vitaro, Tremblay, Park, Cote, Beasley, Algan (2022). "Early lessons in social skills and self-control bring lifelong benefits" Centre for Economic Policy Research, 2022. This long-term study followed a group of boys with behavioural problems who were given social skills training in the 1980s. A recent follow-up showed that this programme led to a cascade of lifelong effects: one dollar invested in this programme at age 8 led to an estimated $11 in benefits at age 39.