I recall this being a series, but it may be a stand-alone book — in it a boy gets a magic pencil from his uncle that will only allow him to write correct answers even if he tries to write the wrong answer. He is ready for a big test, then his dog chews the pencil. In another chapter his infant brother is supposed to be in a TV commercial, but the boy reads the dictionary while watching him and the baby says big words like “grappling hook.” A childhood favorite I would love to share with my daughter!