Calling a child names does affect him deeply. The child responds to a parent like a patient responds to a hypnotist. If you want a kid to be smarter, just tell him he's smart! If he doesn't act smart, then tell him that he's capable of being smart and he should act that way. This concept is developed in depth in my book Raise Your Kids without Raising Your Voice. Perhaps you can get a copy for your husband to read and then he can see whether what I'm saying makes any sense to him. Your husband wants the best for your son and is trying to encourage him. However, he is having the opposite result. The book explains how to get "stupid" kids to smarten up by using the power of positive labels.
Sarah Chana