Big Brothers Big Sisters — National Impact Study
Public/Private Ventures · Multiple US cities · 1992
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
Intervention
Youth (ages 10–16) applying to BBBS community-based mentoring randomly assigned to immediate match or 18-month waitlist. Matches met 3–5 hours per week; volunteers screened, trained, and supervised; matches supported with regular check-ins from case managers.
Assignment
Randomized controlled trial via waitlist; 959 youth at 8 BBBS agencies across US
Sample size
959 youth (487 matched, 472 waitlist control) across 8 agencies in 8 cities
Primary outcome
Drug and alcohol use; aggressive behavior; school attendance; academic performance (18-month follow-up)
Effect estimate
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
Decision
Study widely cited in mentoring literature; BBBS expanded nationally and internationally; evidence contributed to MENTOR (national mentoring partnership) quality standards; National Mentoring Resource Center uses this study as benchmark for evidence-based practice
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
Institution
Public/Private Ventures
Location
Multiple US cities
Year
1992
Policy area
Early Childhood
Mechanism
Community engagement