Hi Myra,
You have to let him do this himself, but know he may not and his grades might slip while he learns how to put himself in charge of it. But consider this, if you do for him, he will always need someone to push him to succeed. Children don't learn something from another making them, they eventually have to find the motivation internally and part of them doing that is to leave them to their own devices, and unfortunately, sometimes watch them make poor decisions in the process.
While grades are important the actual grade itself serves only one purpose, it opens doors to better colleges. But the process they go through to get those grades is what counts. My oldest son graduated in the top 20 of an academically competitive prep high school after taking all honors and AP classes - he's two semesters away from being a chemical engineer, still in the top of his class. The second was in the top 10 of his public high school class and is pre-med at a highly selective private college that only accepts 540 kids a year out of 11,000 applications. He also remains in the top of his class. But my third is still trying to get it. Very intelligent, definitely able to do more, but he has issues with motivation. He failed his freshman high school year only because he didn't do homework. He's currently in an alternative district program helping him make up the lost credits so he can graduate with the rest of his class on time. My last is like his two oldest brothers, highly motivated and succeeding in the 4th grade. Why three got it and one didn't, I have no idea. But I know I won't do for the third. I did for a long time, all the way through 8th grade while I'd never had to do for his two older brothers. What I finally realized is I would be doing for this child the rest of his life because he hadn't found that place inside of him to do it. I should have let him fail earlier, but it broke my heart to think of him not succeeding. Sometimes we have to let them though.
When baby birds first fly out of the nest the mother flies below them to catch them if they fall. She doesn't flap their wings for them, or fight with them to fly. She lets them do it themselves and watches, always ready to rescue them if they need it. I think we human mothers can learn a lot about teaching our children independence by watching mother birds.
Don't do for your son Myra, or be the one who is more concerned about him succeeding than he is. Let him get it himself, and you'll find a remarkable man calling himself your son someday. For me, my greatest reward has been meeting those men, and knowing they became who they were on their own because that means no matter what the situation, they have it inside of them to succeed because they've found their success themselves. Though my third is struggling, I have faith he'll find his way too, it's just taking him longer to get there. But he will, and as hard as it is to watch him struggle and just fly below him, I know I have to so he can succeed beyond school, and in life.
Good luck to you!