Researchers David Dubois and Carla Herrera reported interim results of a national RCT of Big Brothers Big Sisters (BBBS) Community-Based Mentoring Program. Quick take: High-quality RCT finds sizable reductions in youth arrests and substance use over 18-month follow-up.


  • BBBS of America is the largest mentoring organization in the U.S. Its Community-Based Mentoring program matches at-risk youth with adult volunteer mentors from the surrounding community. Mentors & youth are expected to get together regularly for at least 1 year to engage in activities of their own choosing. The program cost is roughly $2,000/youth.

Study Design:

  • The RCT sample comprised 1,358 low-income youth at 17 BBBS agencies nationwide — average age 12, 69% Black or Hispanic, 63% male, average family income about $30K/year.


  • Over the 18 months following random assignment, the study found statistically significant reductions in the rate of arrest (5% Treatment vs 11% Control) and substance use (10% T vs 17% C). It also found modest reductions in delinquent behaviors but these were not statistically significant - so are only suggestive.


  • Based on careful review, the RCT was high-quality (e.g., low attrition, good baseline balance, key outcomes pre-specified). A limitation is that outcomes were measured via youth or parent report, so may be vulnerable to social-desirability bias (e.g., desire to please mentor or program).

  • Future reports, including a 4-year follow-up, will address this by using official arrest records to measure crime. Overall: I think these findings are highly promising but not yet conclusive pending confirmation of results with official records. Disclosure: my former employer, Arnold Ventures, funded this study.

  • PS: Importantly, these findings largely replicate positive findings from a sizable RCT of @BBBSA in the 1990s, as discussed in this more detailed evidence summary.

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