Invite a child to step away from the group when his emotions are escalating. Even if he hasn't lost his temper, ask him to come to another part of the room with you. Interact with him for a while until he calms down. Play with a toy or find another way to distract him.
Remove an unruly child from her playmates and require her to sit in a corner until she is able to control her temper. Gently tell her that when she is ready to play nicely, she may rejoin the group. Keep in mind that many experts think that children should not be made to sit longer than a minute per year of age. Young toddlers do not have much of a grasp on time, so three minutes may feel like 30. The important thing is for her to learn that she needs to control her emotions and respect other playmates, so even if she is only removed for a minute or so, you are helping her to learn self-control.
Set a good example as teacher. This is perhaps the most important thing you can do to teach self-control. If your preschoolers see you lose your temper and lash out at a child or another worker, then you lose credibility when trying to teach them about the importance of behavior management.
Reinforce good behavior. Praise children for sharing toys and other kind acts toward playmates. Call attention to good behavior, so that other children notice when their peers are setting a good example of behavior. Articulate what the child is doing well so that other children understand. For instance, say, "Grace, thank you for sharing your toy giraffe. You are very generous."
Consider a child's needs when they lose self-control. Sometimes, it is OK to ignore mild tantrums. A child may behave well all day but be tired and hungry in the late afternoon and start to act up a bit. Rather than scolding him or punishing him with a timeout, you may want to take him aside and try to comfort him with conversation or play.