Friendships are crucial to children's learning, but their significance in education and wellbeing may be overlooked by teachers.
The finding has emerged from two ongoing inquiries into childhood: the Good Childhood Inquiry, run by the Children's Society, and the Primary Review, led by Robin Alexander of Cambridge University. They were the subjects for discussion at a conference in London this week, hosted by the General Teaching Council for England (GTC).
Both inquiries were set up partly in response to growing anxieties about children's lives. They have found that youngsters have very different concerns from adults regarding the state of modern childhood.
Fears about violent computer games and the pressure of tests were more likely to worry adults, while children said friendships, bullying, and having a say in their lives and learning were among their uppermost concerns.
Judith Dunn, a professor at the Institute of Psychiatry and chair of the Good Childhood Inquiry, has said research shows friendships are vital to children's wellbeing and development at all stages in their lives.
However, a YouthTrends study, funded by the Nuffield Foundation, has shown that since 1986, the number of teenagers with no "best friend" has increased from around one in eight to about one in five.
One submission to the inquiry suggested a re-evaluation of teacher training to include "the ability to promote co-operation and friendship between students".
In a paper for the Primary Review, Christine Howe and Neil Mercer of Cambridge University said that while children learned well by working in groups or pairs, teachers did not always organise the activities to produce the best results.
"Friends working together are more likely than non-friends to engage in interaction where knowledge is shared, ideas are challenged, evidence is evaluated, and options are reasoned about," the paper said.
Initial research from the Primary Review had suggested that the policy of testing in schools was leading to the "scholarisation" of childhood.
A report last year for Unicef, the United Nations children's fund, suggested British children had the worst levels of wellbeing in Europe.
But Professor Alexander said it was important to distinguish the perception of "loss of childhood" from the reality. "The Review's evidence to date does not support the view that England is a nation of miserable children," he said. "It was adults, especially parents and teachers, who were most worried.
"There is a need to move from a negative view of children as victims, problems or threats, to a positive one which celebrates and builds on what children can do. We need to engage with and listen to children, not just talk at them."