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!
Here you go. Is this it?
The Magic Pencil?
http://www.amazon.com/Magic-Pencil-Pirate-Ship-Kraken-ebook/dp/B00L2II7E0
Don’t remember which one it is, but the pencil one sounds like a chapter in Hazel Hutchinson Wilson’s Herbert series from the late ’50s. Herbert has various unusual adventures, he collects tin cans, tries to speak in rhyme, takes magic vitamins, grows a gumdrop tree, etc. I remember the pencil one, it was a purple pencil with a star on it and always wrote the correct answer; when he loses it he runs all over town trying to get it back. You’re right about the dog part.
Don’t recall the part about the baby and the dictionary, maybe part of a similar series? Hope this helps.
That’s it! Thanks so much, this has been driving me crazy for a long time. I appreciate it!