Big Brothers Big Sisters

Updated: Feb 26, 2026
Evidence Rating:
Near Top Tier

Highlights

  • Program:

    A widely implemented community-based mentoring program for disadvantaged youth.

  • Evaluation Methods:

    Two well-conducted randomized controlled trials (RCTs), each with a multi-state sample of over 1,000 youths averaging 12 years of age.

  • Key Findings:

    The more recent RCT (Study 2, below) found 20-40% reductions in youth substance use and delinquent behavior four years after study entry. The earlier RCT (Study 1) measured a much broader array of outcomes and found beneficial effects on a sizable subset, especially in the areas of substance use and education, at follow-ups 18 months and 21-23 years after study entry.

  • Other:

    Both studies have limitations that make their findings, taken together, highly promising but not definitive. Limitations include, for example, (i) the risk of chance findings in Study 1 driven by the large number of outcomes examined; and (ii) sample attrition in Study 2 that was somewhat higher in the program group than control group, potentially undermining randomization.

[Disclosure: Arnold Ventures provided funding for one of the two RCTs (Dubois, Herrera, et.al.).]

Big Brothers Big Sisters of America is the largest mentoring organization in the United States, with over 230 agencies serving 109,254 youths nationwide in 2020. Community-Based Mentoring is the organization’s flagship program. The program matches youth age 6-18, predominantly from low-income, single-parent households, with adult volunteer mentors who are typically young (20-34) and well-educated (the majority are college graduates).

The youth’s parent/guardian applies for his or her child to be matched with a mentor through a written application and child/parent interview. Potential mentors are screened by a Big Brothers Big Sisters caseworker through a personal interview, home visit, and criminal, background, and reference check to ensure that they are not a safety risk and are likely to form a positive relationship with the youth. Prior to a match being made, the youth and parent meet with the potential mentor; the match’s completion requires the parent’s approval.

The mentor and youth typically meet 2-4 times per month for at least a year and engage in activities of their choosing (e.g. studying, cooking, playing sports). The typical meeting lasts 3-4 hours.

For the first year, Big Brothers Big Sisters case workers maintain monthly contact with the mentor, as well as the youth and his or her parent, to ensure a positive mentor-youth match, and to help resolve any problems in the relationship. Mentors are encouraged to form a supportive friendship with the youth and not seek to modify the youth’s behavior or character.

The program’s total cost per youth is approximately $4,000 to $6,000 (2026 dollars), based on the estimates described in the studies below.

Click here for the Big Brothers Big Sisters website.

To see our full evidence summary:
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References

http://www.bbbs.org/ (Big Brothers Big Sisters website)

Study 1

Grossman, Jean B. and Joseph P. Tierney, “Does Mentoring Work? An Impact Study of the Big Brothers Big Sisters Program.” Evaluation Review, Vol. 22, No. 3, June 1998, pp 403-426, linked here.

Tierney, Joseph P., and Jean B. Grossman, “Making a Difference: An Impact Study of Big Brothers Big Sisters.” Public/Private Ventures, 1995 (reprinted 2000), linked here.

Bell, Alex and Neviana Petkova, “The Long-Term Impacts of Mentors: Evidence from Experimental and Administrative Data.” 2024, linked here.

Study 2

Dubois, David L., Carla Herrera, Julius Rivera, Vanessa Brechling, and Staci Root, “Randomized Controlled Trial of the Effects of the Big Brothers Big Sisters Community-Based Mentoring Program on Crime and Delinquency: Interim Report of Findings,” 2022, linked here.

Dubois, David., Carla Herrera, Julius Rivera, Vanessa Brechling, and Staci Root, “Randomized controlled trial of the effects of the Big Brothers Big Sisters Community-Based Mentoring Program on crime and delinquency: Four-year findings.” University of Illinois Chicago, 2025, linked here.

Other Studies

Herrera, Carla, David L. DuBois and Jean B. Grossman. “The Role of Risk: Mentoring Experiences and Outcomes for Youth with Varying Risk Profiles,” A Public/Private Ventures project distributed by MDRC, 2013, linked here.

Herrera, Carla, David L. DuBois, Janet Heubach, and Jean B. Grossman. “Effects of the Big Brothers Big Sisters of America Community-Based Mentoring Program on Social-Emotional, Behavioral, and Academic Outcomes of Participating Youth: A Randomized Controlled Trial,” Children and Youth Services Review, Vol. 144, January 2023, linked here.

Washington State Institute for Public Policy, Mentoring: Big Brothers Big Sisters Community-Based (taxpayer costs only), 2019.Brothers Big Sisters Community-Based (taxpayer costs only), 2019.

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