This is something really small, but its such a distraction. Its when students scoot towards or away from their desks. On a solid floor, depending on the chair, the screech of a chair sliding on a floor surface can directly compete with a teacher's voice. The bottom line is that the less disruptions you have in class, the better.
For whatever reason, students will move their chairs about. It could be simply because at one time, they were comfortable with their chair's position, but now they're not. It could be because they dropped their pencil behind them, need to go grab a tissue, throw some trash away, etc.
Anyway, here's a solution. Assuming that your chair has four feet, grab four tennis balls. Slash them open. You want to be careful not to slash them too narrowly. If you slash them too narrowly, the feet of the chair may not fit. At the same time, you only want to slash it enough so that the feet will fit in the tennis ball. That is ideal. And, this is what you get: