from Figuring Boys Out by Judi Miller, 1982, Scholastic Book Services:

"Duck! He Probably Likes You!"

"Boys sometimes say with their hands what they can't express with their mouths. The say they like you by hitting you!...It's just a phase boys go through...They hit you because they like you. Just think about this: hitting is easy to understand. When boys graduate from whacking you to confusing you with words, it's not such an each puzzle to put together."