I have had a least one student in every class who tries to answer questions asked by another student. Usually they are correct with the answer but the student asking the question mentions to me that they would like the answer given by me not the other student. Eyes roll, darts fly every time that student jumps in to answer. It gets touchy because I want others to participate without having to deal with the know-it-all. I even resorted to handing the white board marker to that student and sitting down in a desk and telling her/him to go ahead and teach the class. They always back down. I know "passive aggressive". I'm not perfect. Any suggestions?