The first thing a parent can do is to become educated about bullying. Find out what your child’s school policy is on bullying. Bullying occurs with adults as well and can be learned by a child simply through watching their parents' interactions with others. It can also be a way to cope with fear. Fear that if another person’s weaknesses are not brought to the attention of others then one’s own shortcomings will be targeted.
Second, acknowledge your child’s feelings about being bullied and help them come up with ways to problem solve the conflict on their own. This will assist them with future conflicts they come across and will be a skill that will serve them well as an adult. If the bullying is severe and is interfering with your child’s well-being and ability to thrive at school, then contact your child’s teacher or principal.
Also consider getting your child a clinical professional, like a social worker or a counselor to talk to. Professionals like these know how to screen for depression and suicidal thoughts that can often be associated with severe school bullying.