School/education serves three purposes in my opinion.

One is to provide knowledge, learning, information and other instances skills, critical thinking.  Although I would say that our school system sorely lacks on this front now and standards of education and knowledge have really diminished.  

Two is economic reasons. The reality is that most people who go to college do it to make more money.  Either just that piece of paper and also a high school degree(vs not having one) means that you will earn substantially more money in your life time. Also you might learn something or more likely from your experiences and what you make of college have some sort of skill that you carry on with you.


Three,  Indoctrination/brainwashing. Society uses institutions(which school/higher education is) to condition people and you could argue in some ways this conditioning is positive at least for the 'society'.  If everyone has a certain standard, they agree(or are forced to out of fear of consequence/shame) to follow certain norms that makes it easier to get along and also for the society to be more productive right?   Education basically conditions people and their behavior and it prepares them for a long life working and being compliant with the government/society/systems.  Even if some tolerance/dissent is allowed it is just that, it's allowed so that can people say what they think and discuss instead of acting on it and to create the illusion that the society is open when in reality the institution and principals and rules of society are very rigid are considered the 'right' ones.

Also college engages in brainwashing students as well now, although this is more political and in my opinion because of a political faction that has a large influence in college and so now people are brainwashed to have a certain ideology and allegiance based on that ideology