There are many aspects of school that the movie focuses on. Let me list a few of them.
Perhaps the most important theme is the theme of respect. As you may recall, Mr. Thackeray, at one point in the movie, tells the class that he will treat them as adults. This was one of the turning points, because through this action, he wins them over. The basic message is that we should treat others with respect and through this action, we may gain respect.
There were also other lessons, such as the importance of looking proper. This comes out most clearly in the outing to the museum. Other lessons were on the importance of speaking properly. Finally, there was also an important undertone of the importance of learning. All of these lessons helped the students to become better people.