help your son, you need first to figure out why he can't pass the exams. If you doubt he has learning disability, you'd better take him to see doctor. If he is proved to be normal, then the reason he has trouble with school is very likely to be that he doesn't know how to study efficiently. Or maybe there are other reasons that discourage him from loving study. You need to dig out the reasons before help him to improve. Many kids are slow when they are in elementary school, but they turn out to be very good students later on in high school.
Maybe we can help you to find out some good ways to treat you son if you know the reasons. Please encourage him and show your love and confidence on him as often as ossible.