http://stopbullyingnow.hrsa.gov/
http://kidshealth.org/parent/emotions/behavior/bullies.html
http://www.areyoubeingbullied.com/page9.htm
If you suspect that your child is being bullied at school, then you need to trust your instincts. Schools are a great place for bullies to build their reputation of power and control.
First, let your child know that you believe that something is wrong. Don't try to "bully" the information out of your child. Be patient. Promise that you will not make the situation worse. Do not promise to keep it a secret, or that you will not report the problem. Do promise that you will not do anything without your child knowing what you are going to do. Be sure that your child knows that this situation will not get better on it's own, and that appropriate adult intervention is needed.
Second, contact the school, once you know what the issue is. Before identifying yourself, ask what the school's policy is on keeping kids safe once they have reported a bullying incident. Do not give out any information until you have a satisfactory answer to that question. If the school does not have an answer for you, ask when you can call get to get an answer. Do not go charging into the school demanding justice. This will only make the situation worse for your child, and will likely embarrass him or her.
Third, set up a meeting to problem solve your way through this situation with your child and members of the school faculty, including the teacher and the counselor. Your goal must be getting this situation solved, rather than seeking revenge. This is a highly emotional time for parents, and there is NOTHING tougher than seeing your child hurting because of another's actions. Your child deserves to feel safe and welcome at school. Be sure to keep that the focus in the meeting.
Finally, once a plan has been set, check in with your child regularly, and the school periodically. Keep in touch with all of the support people. Trust your instincts with your child, and let the school know if the plan is not working,