Maybe it's because of the teacher. Sometimes students and teachers may not have such tacit understanding, which will form a hostile relationship. Then the old teacher doesn't like children, and the children will challenge and resist the teacher by not studying.
The most important thing is to communicate with children and tell them to understand that learning is a violation of nature. Everything that goes against nature is not so happy, not so happy. It is said that it is against nature for adults to go to work, so it is very hard to go to work. The same learning is also an inverse linear behavior, so learning will not be so happy, if it is completely in line with nature. Then children like humans should learn to climb trees and hunt, and play happily in trees like monkeys in primitive society every day. But in that case, we can't adapt to the life in the present society.