Most teachers find it unsettling to observe a student leaning back in his chair, with only two legs of the chair in contact with the floor. Focusing on teaching a lesson can be difficult when a student is teetering on the brink of a dangerous fall. The concern, moreover, is not unwarranted; a chair tipper can easily tip his chair too far, fall over backwards, and hit his head.
Students often lean back in their seats because the chairs are hard and uncomfortable and they're expected to sit in them for long periods of time; leaning back is their way of stretching and releasing excess energy.
Chair tippers often are unaware of what they're doing, which can make it a hard habit to break. Chair tipping is not, however, a behavior you can ignore; there's a real risk that the student will fall. To break a student of this dangerous habit, you need to help him become more aware of what he's doing and then take measures to make him stop.
WHAT YOU CAN DO
Establish a "no tipping" policy. Make sure students understand that chair tipping is not allowed. Point out how easily they can fall over and hurt themselves. If possible, cite examples of students who have fallen. Explain the consequences for chair tipping in your classroom, which might include having their chairs taken away or missing recess.
Give chronic chair tippers other opportunities to stretch and release energy. Some students tip their chairs back in an attempt to move around or stretch. If you have a student who frequently tips back his chair and you conclude he needs to vent excess energy, allow him to get out of his chair more often. You might even allow him to work standing up for a few moments, perhaps leaning against a wall as he writes on a clipboard or reads a book.
Address chair tipping immediately. Do not ignore a student who is rocking back and forth in his chair; chair tipping raises safety concerns and demands an immediate response. Your first reaction should be to tell the student to stop; a simple "Andrew, all four chair legs on the floor, please" may be all that's necessary.
Consider taking away the student's chair. If the problem persists, you might take away the student's chair and have him stand -- for a few minutes or for the remainder of the lesson. Explain that removing the chair is not punishment, but a safety measure, and that you will give it back when you believe he can sit in the chair without tipping it. If the student seems excited about standing, ignore him; eventually he'll tire of it.
Enlist the help of all your students. Explain that you don't always see a student who is rocking in his chair; ask your students to help out by giving a gentle reminder to any classmate they see tipping back his chair.
Praise "non-tipping" behavior. When you see a student who is prone to chair tipping sitting properly, acknowledge that behavior. Find occasions to praise other students who are sitting safely. In that way, you convey to the chair tippers that sitting appropriately is an effective way to attract your attention.