In 10th grade we had this teacher named Gladys Lindes who was more interested in pushing her social agenda than in teaching us world history, which is what we were supposed to be learning. We weren't pleased with this. She was also really gullible for pranks. April Fool's Day was the first day of our third trimester (everyone else calls them "quarters").
Since there was no way to organize a good prank in advance, and since I was stuck at home the entire week with nothing to do, I found some Ivory Soap in Mom's linen closet and asked her if I could use the linoleum carving set Grandpop had given me and try to carve stuff. Keeping a teenage kid occupied and out of trouble is always A Good Thing, so of course they said "Yes."
I spent a couple of days with the carving kit, the soap, and "models" of Mrs. Lindes's An-Du-Septic chalk (the special anti-dust stuff used in schools) hidden in my desk drawer. Having no real privacy in that house, I instead took advantage of being 15 years old and acted like I was being "an ar-TEEST" to throw my parents off.
"What's that you're making?" Dad would ask.
In an eccentric-sounding tone, I'd reply, "Oh, I dunno...I'm letting my hands do the work. It's a surprise."
"It kind of looks like the 'Flintstone mobile,'" Dad might say.
"You're right, it does. How could you guess?"
The next time he'd come up it would look like something else, and the dialog would be remarkably similar.
"It kind of looks like logs."
"You're right it does. The 'Flintstone mobile' didn't quite turn out right, so I decided to do something else."
"You could make a log cabin like the one Abe Lincoln had."
"Why, yes! I could."
The only thing that kept me from bursting out laughing was the thought of getting the snot beaten out of me if Dad had figured out what I was really up to.
Eventually I finished my supply. Due to a combination of thoughtfulness and clumsiness (the damned soap kept breaking), I had a mix of long, full sticks and nibs of various sizes. I crumbled a little of the An-Du-Septic chalk pieces I had and rubbed the dust on the outside of the soap-chalk pieces to make them feel more like The Real Thing. After my parents had gone to bed and turned the lights out, I went downstairs "to fix myself a snack" and grabbed a plastic bag for my "creation," carefully tucking it deep inside my purse so my folks wouldn't see it as I was leaving.
Taking no chances, I slept with my purse under the covers and took it to the bathroom with me the next morning. I somehow made it out of the house without anyone noticing it was a little "fuller" than usual.
When I got to school, I was able to shuffle things around so the bag was at the top of the purse. As we waited for the previous class to end so we could go into Mrs. Lindes's classroom, I divulged my plot to my classmates.
Holding up the baggie, I asked, "You know what this is?"
One classmate replied, "It's chalk. Big deal."
"No. It's Ivory Soap."
"What???!?" Several classmates turned around, and suddenly I was The Most Popular Person In School. They picked up a few pieces of the soap-chalk and were duly impressed. We then conspired that they would distract Mrs. Lindes while I swapped her chalk out for my soap-chalk, then would take up all the seats so I'd be forced to sit at the desk where she kept her "archive" supply of chalk, making it easier for me to swap in mine. As her back was turned, I swapped chalk, starting with a nib she had marking her place in our textbook.
Several times in class she went to write on the blackboard and stopped. A sea of faces turned bright red each time she turned around and raised her had to write, only to stop and turn around and continue lecturing.
Finally she went to write. Nothing. She picked up another piece and it didn't write, either. "What happened to my chalk?" she exclaimed as she stomped her feet and flailed her arms. Next she went to the first piece I had swapped out (the one in the textbook). It didn't write, either.
As we clamped our mouths down really hard, trying hard not to laugh, she then went to the desk where I was sitting and frantically dug through the archive supply to my left. I'm told my face was a lovely shade of burgundy as I fought back hysterical laughter. Of course, that "chalk" didn't work, either. Finally she dug out her purse, dug out her keys, unlocked the closet in her classroom, and dug out some real chalk. The entire episode kept us from having to put up with about 15 minutes of her irrelevant-to-world-history drivel.
She never did figure out who did it, either. When I found out at the end of 11th grade she wasn't coming back, I decided I'd tell her on her last day. She had no idea it was I who'd done it.
The best part about the prank? No mess to clean up at the end. When you sponge the blackboard the way you normally do, it cleans up by itself.