Does the school system have a net positive or a net negative effect on children? ...

Compared to unschooling or home schooling them?

Or does it just depend on the child, the family and the school involved?

Clearly, formal schooling introduces the child to a wide array of people, but this can include negative and disruptive influences, and can result in bullying and negative projections that can impact negatively on the child's self-esteem.