This is driving me nuts!

I have seen a LOT of movies and I’m usually really good with actors and movie names. This movie has popped into my head and I can’t figure it out. Its a movie from the 80s or early 90s. What I remember most is An old man, the grandpa, makes a wish to know the answer to every question and at the end of the movie his wish comes true. He’s not the main character if the movie but at the end a house gets destroyed and the go to a school theater that is being worked on and someone asks where the hammer is and the grandpa k owe exactly where it is.