Big Brothers Big Sisters is a community-based mentoring program that matches an adult volunteer, known as a Big Brother or a Big Sister, to a child, known as a Little Brother or Little Sister, with the expectation that a caring and supportive relationship will develop. The match is well supported by mentor training and ongoing supervision and monitoring of the mentor relationship by a professional staff member. Ideally, the matched pair spends three to five hours per week together over the course of a year or longer. The activity goals are identified in the initial interview held with the parent or guardian and the child. The top priority is for the matched pair to develop a relationship that is mutually satisfying and provides contact on a regular basis. The goals established for a specific match are developed into an individualized case plan, which is updated by the case manager as progress is made and circumstances change over time. The case manager is responsible for maintaining contact with all parties in the match relationship.

In order to ensure effective matches between volunteers and youth and to monitor program quality, the professional staff screens all applicants, youth, and their families. Orientations are conducted with youth and volunteers, and training is provided for volunteers. Staff supervises matches between youth and volunteers by contacting all parties within two weeks of the initial match and then having monthly telephone contact with the volunteer for the first year of the program. The staff also contacts the youth directly at least four times in the first year.

An experimental design using random assignment was used to evaluate the Big Brothers Big Sisters program at eight program sites: Phoenix,