Among middle-school students, friendships can make the difference between good and poor grades.

Researchers studied 1,278 students who were asked to name their three best friends. The researchers then examined the academic and behavioural records of those friends.

It was found that students whose friends are socially active in positive ways got better grades, while those with friends who behave badly got lower grades. In addition, having pro-social friends and also staying away from deviant peers was associated with even higher grades than simply being friends with high-achieving students.

The researchers suggest that parents and teachers should pay special attention to changes in students' friendships at this age. Parents should pay attention to what their children are doing and with whom they hang out. If parents notice that there is a shift in a child's friendship network, they should try to get to know those children, talk with teachers and communicate naturally with their own child about where they are going and when they will be coming home.

The researchers also urge adults to help children get involved in adult-supervised activities because these can help encourage pro-social relationships.