Dear Know-It-All: Read All About It! is great reading for you if you are having issues with friends. It helped me solving some problems with friends of mine own.
It is about a middle school girl who gets picked as the "know-it-all" for an article in a school newspaper. She receives unsigned letters from students with problems they are dealing with at school and she has to find a way for them to solve these problems.
Find out how she resolves these situations . . . probably some of them are already familiar to you!