Let's assume this is not because of a medical or physical problem and is not due to a severe emotional or mental illness. If these were the causes, they should be being treated and arrangements should have been made for the child's education.
Often missing school is the next step beyond not caring. The young person only goes to school when someone makes him go. He might go if he has nothing better to do. And he thinks almost anything is better. Skipping school finally leads to dropping out or getting expelled.
By now, you see how it works. Learning problems keep a child from being successful at school. He tries but does not succeed. Over time, learning problems turn into behavior and attitude problems. These lead to severe stress and very low self- esteem, and in turn to not caring and often to dropping out. At each step along the way, it was easier to blame the child and hold him responsible than to understand and help.
If your child has any of the problems discussed above, talk with his teacher about your concerns. They are serious and need attention now. If you do not start now, the problems will still be there when school starts again next year and when it starts the year after that.
Perhaps you do not have time to talk to your child's teacher. If not, that is a real shame. Your child will have the rest of his life to deal with the consequences of your being too busy to help him today.