I told you!

 Many people in class doesn't sit properly, and they can can hurt their backs. Teachers do not allow studients to have a bad posture in class, they correct them to sit well on their chair. The good posture consists of putting all your back on the back rest of the chair, this can help you to have a good health for you and your back. I know people that have those problems and they got hurt, so take care about your health having a good posture on the chair.