Mentor programs such as Big Brothers Big Sisters can make a big difference in the lives of at-risk youth, boosting their self-esteem and reducing the chances that they’ll get involved in violence, drugs, or alcohol abuse. But the loss of a strong role model can devastate an already-disadvantaged youth. A new study may help predict which volunteers are likely to keep a long-term commitment to their protégés.

The study, published in the March Journal of Applied Social Psychology, found that adults who rated themselves as similar in personality to their little brothers and sisters were most likely to maintain long associations. Currently, the average match lasts about 22 1/2 months, according to Big Brothers Big Sisters.

Researchers Catherine J. Lutz, of the University of Dayton, and Benjamin P. Madia interviewed adult participants and compared the adults’ initial expectations for their relationships with their protégés with how much the volunteers actually liked the kids afterwards.

According to the report, mentors who considered themselves akin to their young charges in extroversion or introversion stayed in the program longer than those who felt that they were mismatched. Lutz attributed this to differences in how each person prefers to spend his or her time. Outgoing adults and children, Lutz said, probably enjoy going to large social gatherings, while quiet types may prefer long walks in the woods.

The study also found that volunteers who joined Big Brothers Big Sisters with the highest hopes for having an impact on their young charges might be setting themselves up for disappointment. Ironically, Lutz said, “Those mentors with the most ambitious ideas about how much they will influence their protégé may ultimately be the least likely to follow through with the program long enough to have a real impact on the life of the child they set out to help.”

Sherry Squire Mitchell, executive director of Big Brothers Big Sisters of San Francisco & the Peninsula, was not surprised by Lutz and Madia’s conclusions. She noted she sometimes gets applicants who ask for a certain type of child.

“A Big Sister might say, ‘Gosh, I’d like to have a really shy little sister because I was shy myself and I think I’d be able to work with her,’” Mitchell said.

Read more stories by Casandra Lewis & Andrew Nelson.