Thank you, all of you! Turns out he didn't need much explanation. I just told him he was going to meet Dr A and she was going to ask him a bunch of interesting questions to find out how he learns. He asked if it would be questions like "what is 40 plus 40", and we just moved on to doing some math together. No other questions about seeing the doctor. I'm now sitting in the waiting room and I hear him having fun in there. Regardless of what comes out of it, we'll likely understand more about our little monkey! 😀