Imagine the scene: it's 8.30 a.m. and a small group of schoolchildren have called over to a classmate's house to ensure she turns up at school today. The night before, another group felt compelled to ring a classmate to check that he was doing his homework.

What's going on? Why are these kids so concerned about other students' performances? The answer - co-operative learning.

The concept has been around for years, but it has been developed in recent times by two brothers, Professors David and Roger Johnson. They run the Co-operative Learning Centre at the University of Minnesota.

According to David Rogers, co-operative learning has a number of spin-offs for students, including increased empathy and care and consideration for other people. In the United States, where co-operative learning is a popular method of classroom management, students really do call and check that classmates are doing their homework or ensure that they make it to school on time, he says.

What then, is co-operative learning? It involves splitting up a class into learning teams which can consist of two, three or four students. "The students have two responsibilities," says Johnson, "first, to maximise their own learning and, second, to maximise the learning of everyone else in the group."

It's vital that students are randomly assigned to groups. "It's important that you get a heterogeneous group, especially if you have disabled students or students from different social classes," he says.

Any lesson can be structured for co-operative learning. Take maths, for example - the students are given a set of maths problems. The groups work though the problems. The next day students are tested individually on the problems. If students perform poorly, their groups are called to account and have to work out ways of ensuring that all members of a group thoroughly understand the maths problems. "This creates a peer support system which ensures that every student does his or her best," explains Roger Johnson.

"To meet the challenges of education and succeed, students need a support system - someone to explain, encourage and keep them going. The teacher, who in a 50-minute class of 30 students, has less than a minute and a half to spend with each pupil, hasn't the time."

All the research, he says, shows that high-achieving children who help lower-achieving children end up scoring higher marks than high achievers who work alone. "In teaching material to others you clarify it for yourself - it's the teacher who gets the most out of it."

Research on different learning styles - co-operative, competitive and individualistic - indicates that co-operative learning results in higher achievements and greater motivation to learn, he notes. Competitive and individualistic learning both have negative effects on many students.

Working alone can make you selfish, while working competitively can demotivate some students, who eventually drop-out. This is particularly true of youngsters from dysfunctional or poor families who have few chances of winning. They may have to compete with rich kids who enjoy the extra benefits of home-support or tutors, grinds and summer camps.

Co-operative learning improves personal relationships and reduces racism, sexism and stereotyping. Students retain their learning and enjoy higher reasoning skills. Co-operative learning encourages self-esteem and the ability to deal with stress and adversity and thus promotes greater psychological health, he says.

But, he stresses, "there's nothing magic about a group. They can be extremely destructive." It's vital that group members believe that they are accountable and must contribute to the welfare of the group.

Before co-operative learning is introduced in a classroom, teachers need training. "Teachers have to create a sense of positive interdependence within the group - a sense that students sink or swim together and that they all benefit if the group succeeds. They have to inculcate a sense of individual accountability - that each student must do his or her fair share and nobody gets a free ride.

"Promotive interaction - that is that students promote each other's success by helping, explaining and encouraging - is another vital aspect. Teachers, too, have to teach social skills including interpersonal, small group, leadership, communication and conflict management skills.

"Finally teachers must encourage groups to reflect on how effectively they're working together and how they can improve." Having untrained children trying to work together can be chaotic, he warns. "They need management training and the teacher must provide that."

The future lies in teamwork, Roger Johnson argues. "If you want really outstanding and creative work - it comes out of working in teams. To do anything worthwhile you have to be part of a team. You don't become President or head of a big corporation by being a highly competitive loner."