First, students get to know how to live by with people in the classroom. For over 10 years, students ceaselessly communicate and interact withe lots of friends and teachers. By doing this, they naturally acquire some kind of norms about what they should do and should not do. This is essential virtue even if they graduate from the school, because we are living in the world where we cannot live alone.
Secondly, students learn the way of thinking in the school. Some might say that a lot of subjects finally become useless in real life. However, every subject involved in education requires student to think logically, critically, and creatively. Even a little thought on a daily incident is a result of an acquired ability to think, which is from the classroom. For example, people naturally find the shortest way when they go to somewhere and think about a solution when they encounter an article. All these features cannot be internalized if students does not go through necessary education.
To sum up, I think that students learn the most fundamental things in the classroom in terms of sociability and intelligence.
감사합니다!!