MumOfThree, I have a funny story to relate along those humor lines...
When my son (now 8) was in Kindergarten, his teacher pulled me aside at pickup one day and said she was having a problem with him. She was clearly distressed to be telling me this, since she loved my son and didn't understand his "misbehavior" in this case. She said he was laughing at kids who got the answers to her questions wrong (e.g., 2+2=5), and it was so unlike him to tease. I knew right away what was happening, though. I told her that most likely, he thought the kids were joking! To him, it was unthinkable that anyone wouldn't know that 2+2=4, so OF COURSE the kid was trying to be funny! And, like your child, he thought this was the best form of humor EVER!
I had a talk with him that night about different ability levels and it never happened again.
