It's No Joke! — Carolyn Keene

SOMEONE'S PLAYING PRACTICAL JOKES -- BUT MEAN MR. DALY ISN'T LAUGHING!
Nancy's class is going to the zoo on Friday, but first they have to survive a week with their strict substitute teacher, Mr. Daly. And things aren't looking too good: someone is playing practical jokes on him, and he's threatening to cancel the trip!
First a sign saying OLD MEANIE is taped to his back. Then someone puts a fake goldfish in his water glass. But who would want to miss a fun trip to the zoo? If Nancy doesn't find out, the joke will be on the whole class -- and that's not funny!