During the first week of school back in August, I had about ten of my new little darling students (now not as little or as darling) tell me that I don't need to bother to plan an April Fool's joke on them - they already were aware of all my tricks. (Last year I told my students I was engaged... then later, after all the jokes were over, they took a test they had to pass to be able to pass 3rd grade.) So, naturally, I've put a lot of thought into what I was going to do as a prank!
Yesterday, I had a sub lined up for the afternoon (and not just for the prank, I really had to be somewhere). I told my students right before they left for lunch that I had received a letter that my teaching license was not current, and it hadn't been all year. In order to renew it and not get in huge trouble, I could attend classes for 2 months (1 month if I were willing to go at night as well). Which would mean that I'd miss school for all of April, and possibly all of May! I did have a few who thought this might be a joke... the rest weren't sure. I told them the sub that afternoon was so I could things ready for them for the month, and they went to lunch and I left! I spent a few minutes in my class before leaving, and had one girl come in and say that she was sorry that I was leaving, and gave me a hug! Very uncharacteristic of this student to talk to me about something so personal as my leaving, and to admit that she might miss me... so cute!
This morning when first track came in, they were welcomed by Mr. Grimley, who was going to sub for me while his student teacher continued teaching his class for the rest of the year. I was in the library during this, and stood in the hallway for a few minutes after they came in... silence! Not a word. Such glum little faces! I came in, told them they were all April fools, and we got on with our morning. When second track time came around, first track agreed to buy in and play along to be in on the joke for second track. I came in a few minutes later and got them again! The girl who had come in to hug me good bye yesterday looked awful, like she'd been crying that morning - poor thing! She puts on a tough front, but I guess this got to her a bit.
Don't go thinking I'm all awful... I did get them cookies for being good sports. I also found out that three parents called the principal (I told her about the joke) to see what was going on... she let them in on the joke, and they laughed, thank goodness!
Now I've got to start planning for next year... :)
We made it! I was a little disappointed, though, that there weren't any little China men at the top selling bottles of water for 100 yuan (about $12 when we were there - a regularly priced bottle of water would have sold for 5-10 yuan...). 
