How can I make a parent–teacher meeting useful when my son barely gets a chance to speak?

We had used fourteen minutes of a fifteen-minute appointment when my son said, "That's not why I didn't hand it in." The teacher looked at the clock. I said we'd discuss it at home.

On the way back, he explained that he had misunderstood which draft to upload and then felt too embarrassed to ask after the teacher announced the missing work. He's twelve. I had spent the meeting talking about how long his homework takes and how often I have to remind him. The teacher had shown me the missing-assignment list. Neither of us asked him about that particular piece.

I don't know whether his explanation accounts for the other missing work. It does change what I understood about this one. How do I follow up without sending an email that speaks for him all over again? He says he wants to explain it, but doesn't want me standing beside him correcting his words.