Big Brothers Big Sisters — National Impact Study

Summary

The BBBS national impact study is the most rigorous evaluation of one-to-one community mentoring ever conducted. Across 8 agencies in 8 cities, youth randomly matched with a trained volunteer mentor showed substantial reductions in drug initiation, aggressive behavior, and truancy. The effects were largest for children from single-parent households and for minority youth — the populations most likely to lack access to stable, supportive adult relationships outside the immediate family. The mechanism is social capital formation: a reliable adult relationship that provides modeling, accountability, and a consistent presence in an adolescent's life. The study is notable because it documented these effects with only an 18-month follow-up, suggesting that even relatively brief mentoring relationships can shift behavioral trajectories in adolescence. It became the evidence base for mentoring program quality standards used across the United States.

Research question

"Does a structured one-to-one mentoring relationship with a screened and trained adult volunteer reduce problem behaviors and improve school performance among at-risk youth?"

Methodology

Result

Positive

Drug use: −46% less likely to initiate illegal drug use; alcohol use: −27% less likely to initiate; aggressive behavior: −33%; skipping school: −52%; average GPA: +0.14 points; effects largest for minority youth and youth from single-parent families

Evidence strength

Strong

Randomized controlled trial with large sample.

Replication status

Partially replicated