I would think that as PIC you are still responsible, so even if allowing a student pilot to work the radios, you should be listening to every call and every response. If the student pilot misses something, or says it back wrong, there is nothing wrong with making corrections or clarifications, just don't miss the calls because "he was handling it". I agree that they will take that excuse as a BS answer. You are PIC and responsible tip to tail. This is one example where ****** doesn't roll down hill.