Don't be overly critical when an unaccepted child does something wrong. Criticize gently, accentuating the positive aspects of his behavior. Never single out a child who is having social problems in the classroom. He may be acting out because he is unhappy with the classroom dynamic, and singling him out may only make the problem worse.
Have zero tolerance for bullying or intimidation in your classroom. If one or more children are picking on someone else, intervene right away. In addition, teach your class about how harmful put-downs can be. Go over what negative comments are unacceptable to say, and ask for suggestions about positive encouragement students can give each other.
Come up with structured games and play that involve all students. Avoid cultivating situations that can lead to someone being excluded, especially in group work or gym class. For example, don't let students pick their own teams or groups, as this makes exclusion very easy. Instead, decide on team or group composition yourself.
Identify a friendly child in the class and use him to make another child feel accepted. Pair the two together for class projects. Ask the friendly child to make sure he is included in group games during recess.