This is very common for children with learning problems. If it goes unnoticed, and it often does, they finally get to where they just quit trying.
Think about this. Suppose you had tried for years to learn how to do something and could not learn to do it. Add to this people who keep telling you, "You are not trying hard enough." "You just need to put forth more effort." "You are failing, and some day you will wish you had taken advantage of the opportunity." How long would you keep trying? What would your attitude be? How would you react to those people? Maybe you are a saint; but most of us would probably do and say things we should not put in writing. It may be youngsters who dig in and fight back are the healthy ones. The ones who passively keep trying may have another kind of problem. Whatever you think you would do, trying harder and still not succeeding is very frustrating.
What is wrong? Why is your child not learning, not succeeding? For his sake, find the answer before he joins the ranks of those who just quit.
This is something worth thinking about. With some exceptions, children who do not do well in school are trying as hard as those who are doing well, those for whom school comes easier. It does not take as long to do homework if you know how to do it. It does not take as much effort to read assignments if you are a good reader. "It is not fair. I spent two hours to get a D and others spent less than an hour to get B's. I quit!" Any time your child is not learning, help him find out why. It likely has little to do with anything that will improve just by trying harder.