I used to say “I dunno” a lot as a kid. It was my placeholder. Depending on the situation, it usually meant one of two things: “I genuinely don’t know the answer to that question,” or “I do know the answer, but I don’t know how to phrase it.”
I got into the habit of “I dunno” to questions because other people – adults especially – wouldn’t give me time to construct my thoughts. They figured that if I could blast out entire monologs about weather, I should be able to answer any question instantaneously and intelligibly.
The issue was, for me then and now, it’s a situation of “Fast, coherent, and full – pick any two.” I can answer quickly and coherently if you want an incomplete answer. I can answer quickly and fully if you don’t mind what I’m saying coming out so garbled you can’t make heads or tails of it. But if you want a coherent, full answer to your question, be prepared to wait a while so that I can sculpt the words into what they need to be.
Adults didn’t get this, and they’d get angry if I took too long to answer. So I started saying, “I dunno.” This would also frustrate my parents, especially if it was a preference question or a question I definitely did know the answer to. “What do you mean you don’t know?” or “Yes, you do!”
It would frustrate me, too, because a lot of the time, my parents would take it at face value and then work of the assumption that I didn’t know. “I know that.” “You just said you didn’t!”
One of my teachers growing up had it figured out, though. She’d hear me say, “I dunno” and wait a beat or two. If I moved the conversation on, she knew I genuinely didn’t know, and if I answered fully a few seconds later, she knew I just needed time to process. It worked really well.
So, I’d say, if you’re dealing with a kid whose default answer seems to be “I dunno,” try giving the kid a bit of time to sort out their thoughts before you move on. You might be surprised by how they answer.