• Intervention: A community-based mentoring program for disadvantaged youth ages 6-18.
  • Key Findings: Randomized controlled trial shows sizable decrease in youths’ drug and alcohol use and violent behavior.

Description of the Intervention

Big Brothers Big Sisters’ community-based mentoring program matches youths 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 their 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 case worker 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 for 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 insure a positive mentor-youth match, and to help resolve any problems in the relationship. Mentors are encouraged to form a supportive friendship with the youths, as opposed to modifying the youth’s behavior or character.

In 2008, Big Brothers Big Sisters served 255,000 youths at 470 agencies nationwide. The national average cost of making and supporting a match is approximately $1,300 in 2009 dollars. Click here for the Big Brothers Big Sisters website.


This program was evaluated in one randomized controlled trial of all 1,138 youths, age 10-16, who applied to one of eight large Big Brothers Big Sisters agencies in various U.S. cities between October 1991 and February 1993, met the program’s eligibility requirements, and agreed to participate in the study. Youths were randomly assigned to 1) an intervention group, which agency staff attempted to match with a mentor; or 2) a control group that was placed on a waitlist for the duration of the study (18 months). Big Brothers Big Sisters successfully provided 78% of the youths in the intervention group with a mentor.

62% of the youths in the study were boys, 56% were minorities, and 43% lived in households receiving food stamps and/or welfare.

Effect of Big Brothers Big Sisters on youths in the intervention group, 18 months after random assignment (compared to the control group):

These are the effects on all youths in the intervention group, including those who were successfully matched and those whom staff unsuccessfully sought to match:

  • 46% less likely to have started using illegal drugs (6.2% rate for the intervention group vs. 11.5% for controls).
  • 27% less likely to have started using alcohol (19.4% vs. 26.7%). This effect was statistically significant at the .10 level but not the .05 level.
  • 32% fewer incidents of hitting someone in the previous 12 months (1.8 incidents per person vs. 2.7).
  • Fewer days of skipping school during the past year (0.4 days vs. 0.9 days).
  • Small, marginally significant, positive impact on Grade Point Average (G.P.A. of 2.71 vs. 2.63).
  • No significant impact on the likelihood of stealing or damaging property.

Discussion of Study Quality (click here for a glossary of terms)

  • The study had low attrition: 84% of the original sample completed the 18-month follow-up survey.
  • The study measured outcomes using an intention-to-treat analysis.
  • Prior to the intervention, there were no significant differences between the intervention and control groups in measured characteristics.
  • This was a large multi-site study of all eligible applicants (ages 10-16) to eight large Big Brothers Big Sisters agencies across the U.S., providing evidence of the intervention’s effectiveness under real-world conditions.
  • Study Limitations: First, outcomes were measured through youth self-reports (i.e. survey interviews), and were not corroborated by more objective measures (e.g. school administrative records). Second, although the interviews were conducted by a research team that was independent of Big Brothers Big Sisters, the interviewers were not blind as to whether the youths were in the intervention versus control group. Without blinding, it is possible that an interviewer’s bias (e.g., pre-existing belief in the intervention’s effectiveness) could influence his or her measurement of outcomes. Third, the study only had an 18-month follow-up; longer term follow-up is necessary to determine if the above effects are sustained over time.

Other Studies

One additional randomized controlled trial of the community-based Big Brothers Big Sisters program has been conducted, but we do not describe it here because it falls outside this website’s criteria (due to the short follow-up period and small sample size).


(Click on linked authors’ names for their contact information)