Dr. Greene's Answer
The best way to determine whether or not he has a diction problem would be for a doctor or speech therapist to hear him talk. But if he will not talk at the office, perhaps a videotape would work, so they could get an idea how his mouth moves when he speaks.
They can get some idea from a physical exam (where the tongue-tie connects on the tongue and on the gum line–right on the tip of both is more likely to need surgery), but most kids with tongue-tie do not need treatment. But if there is a question about speech development, it makes sense to have that aspect looked at.