When I stand in front of a class to teach a group of students, I use good posture. I expect the same courtesy from the students sitting at their desks.
Students should sit up straight in their chairs just as they would at the dinner table. They should not lean on the desk with their head held up in their hand. Place both feet on the floor with all four legs of the chair on the floor as well. Do not tilt back in the chair.
Leaning on the desk, holding your head up or lying it down on the desk is rude and disrespectful to the teacher or speaker. If you can’t show respect to the teacher, then perhaps the teacher shouldn’t take the time to share his or her information with you.