Boy, that's a tough call. If he can't do the requirements then he shouldn't proceed on to new material. I'd say let him keep his belt but he will have to learn all of the filler requirements to get him to his rank in your school.
I'm less than 3 weeks away from opening my own school and I hope this doesn't happen to me. I won't be teaching the TKD curriculum so it might be easier for me. Good luck. I'm going to keep checking back on this thread.
I appreciate your thoughts Mr. Farnsworth. I don't plan on teaching him any NEW material, except for the specific one steps that the white & yellow belts know. He'll be 1st poom for a lloongg time.