Big Brothers Big Sisters (BBBS) is a program that matches non-related mentors with children to promote positive development and social responsibility. The BBBS network comprises individual, independent agencies that adhere to very specific BBBS standards and criteria, yet may adjust the program to the specific and unique needs of their communities. In the traditional Big Brothers Big Sisters mentoring model, the volunteer mentor commits to spending approximately three to five hours per week with the child for at least one year. Goals for the child are set with the BBBS staff during an initial interview held with the parent and child.

A relatively new BBBS activity focuses on establishing school-based mentoring programs. These programs differ from the traditional BBBS programs in that all contact between the mentor and the youth takes place within a school and in that they adhere to a different set of participant requirements. Owing to these adaptations, the BBBS school-based model seems to be opening the door to a wider range of participants among both volunteers and youth. Big Brothers Big Sisters in School, a mentoring program that takes place in a school environment and allows weekly breaks from regular programming for the child to take part in one-to-one activities with the mentor, now serves as many children as the traditional community program.

Big Brothers Big Sisters' mission is to provide supportive relationships for young people to assist them in realizing their potential.

In existence for more than a century, BBBS is composed of 440 agencies that served more than 220,000 youths across the country in 2005. The program has been shown to impact a variety of behavioral outcomes without providing a behavior-specific intervention or targeting a specific behavior. The researchers found that, compared with the control group, mentored youths were

- 46 percent less likely than controls to initiate drug use
- 27 percent less likely to initiate alcohol use
- Almost one third less likely to hit someone
- Skipped half as many school days
- Felt more competent at schoolwork and showed gains in grade point average
- Displayed better relationships with their parents and peers(such as academic improvement, drug use, or violence).