This can be a sign of several problems. The most likely is your child has gotten used to only doing his work if an adult is standing over him. He has learned a very bad habit. Self-discipline, self-direction, responsibility, and the ability to work independently are learned. Your task is to teach him skills and habits he should already have but does not.
Another possibility is a need for structure, support, and help. The adult standing over your child is likely to offer suggestions, help keep him on task, and help him organize his work. It seems like your child needs constant supervision but the real need is for help.
Perhaps because of hyperactivity, attention deficits, or other learning problems, your youngster just cannot settle down and do the work. If these causes are there, he will have other problems you will notice.
Whatever the cause, your child's need for adult supervision is real. If you watch, here is what you will notice. He can work alone for short periods. Maybe he can work alone only for ten minutes. Maybe he can only handle three minutes to begin with.
Keep shortening the time until you find an amount of time he can work without you watching him. It will take a lot of patience but is nothing to get upset about or frustrated over. If you do, quit for a few minutes. Say, "I need a break. How about you?"
If you want to teach your child to work independently, positive rewards work best. Start with an amount of time short enough to be sure he succeeds easily. If there are not other serious problems, ten minutes usually works to start.
Say, "If you stay with it for ten minutes right now, you can quit whenever you want after that." The positive reward is getting to quit whenever he wants.
You worry he will not get his work done. He probably will not. It likely will be some time before he finishes an assignment. Learning to do it himself is the first order of business, though, unless you want to stand over him for the next ten or twenty years.