Despite all the talk of socialization, few children actually learn teamwork in school.
Oh, its not that they don't work in groups, but their work doesn't really allow for real teamwork. A team brings people with different capabilities together to accomplish a certain goal. This happens only with sports teams and the band/orchestra but most other teams have pretty much faded away to make more time for getting ready for the test.
In most group learning situations the person who knows the answer hands the answer out to everyone else. When I was in school this was called cheating and hurt the cheater more then the cheatee, mainly because they got the grade but not the knowledge. In some cases the person that knows understands that giving the answers away is not fair, but between a grading system that gives the whole group the same grade and peer pressure they see no other choice. They could try teaching the others but the other students don't believe that the knowledge is all that important or the teacher would actually make them learn it. The fair thing to do is to split all the problems evenly between the student and they each do them. But that is just individual learning, and back where we started and then we still test them as individuals.
I am not sure how this happened but a lot of good teaching ideas just seem to end up reinforcing the idea that knowledge is worthless.
To learn team work you need to have a team, people with different abilities working together toward a common goal.
A sports team is obvious but there are plenty of others.
A band or orchestra, even a garage rock band is a team if they are going to sound good.
A theatre troupe.
Many clubs have goals, in a rocketry club they could build a rocket that is fastest to height or carries the heaviest payload or something. A birdwatching club can do a species survey.
Join a volunteer group or even start a business.
It is differences working together toward a common goal that makes a group a team.