I am no psychologist, but partnerships help youngsters interact with others to achieve a common goal to mutual benefit. It helps to forge understanding of how others work (not necessarily as we would) and good common human interaction possibly reducing selfishness, creating leadership skills and teamwork/subservience and their pertinence in everyday life.

Young people need to understand that cooperation and teamwork make lives a whole lot better! If they are insular, they will not learn to see there are other ways to do things- more than one way to look at things. It helps them see other's point of view. It also will eventually keep them from selfishness and thinking only of themselves, which everyone knows is a healthier view. The younger children start interacting with others and learning proper behavior, the sooner they will develop socially, and that will help them with everything throughout their lives

Together we learn.

On children learning about working partnerships -
Children in group situations often have behavior and self control issues anyway. Smaller kids can appear as vulnerable targets to some who feel annoyed and think of themselves as 'enforcers'. Sharing play things
and school materials, or allowing smaller children/siblings to laugh and
have any fun - is learnable.