I got a new kid a few weeks ago, and to put it mildly, he seems to live in a haze. While he does (surprisingly) possess some math aptitude, he usually doesn't look like he knows what is going on.
Whenever it's time to switch classes, he is always the last one out of the room, no matter what order I call the kids in. It just takes him that long to get his muscles firing and moving, I guess.
So while he and his class -- the class that has JUST left my room -- wait for their other teacher to pick them up, I stand in my doorway and greet my third class of the day. As they come into the room, I stand with my fist out, to give them a fist bump and a "Good afternoon." (I used to do high fives, but switched to fist bumps in the hopes that it would cause less germ-passing. HA.)
My new kid, standing at the end of the line that has just LEFT my room, will quite often see me standing there with my fist out -- and walk over with HIS fist out in an attempt to give me a fist bump and enter my room. I have to gently remind him (more than once, on some days!) that he has already been to my class that day.
At least he remembers his name... most of the time.