Our preschool doesn't do a naught mat/corner or anything, but if there is a child being toublesome or disruptive then the are removed from the group. It's really hard with little ones that age because they still need to learn that when they are at preschool they have to behave a certain way and that if they don't they will miss out. From what I've seen of our preschool over the years they are certainly into discipline as opposed to punishment and explaining to them why they can't do what they are doing.