Tales of a Fourth Grade Nothing, by Judy Blume. Classic! I remember loving these as a kiddo, too. We actually bought all five of these instead of grabbing them at the library. Every kid needs Judy Blume on her bookshelf.
Mrs Piggle Wiggle! My childhood favorite! Mrs. Piggle-Wiggle lives in an upside-down house and smells like cookies. She was even married to a pirate once. Most of all, she knows everything about children. She can cure them of any ailment. Patsy hates baths. Hubert never puts anything away. Allen eats v-e-r-y slowly. Mrs. Piggle-Wiggle has a treatment for all of them.