It can be so frustrating for a parent to know that their child is being bullied and feeling like there is nothing you can do to fix it.  Bullying can be very destructive to a child's self-esteem, so it's important to do whatever you can do to make it stop.  It's great that you're asking for help.
 
If it's the teacher that's doing the bullying you need to go to their supervisor to make a formal complaint.  Typically this means talking to the principal of the school.  Ask your child to write down exactly what the teacher has done to bully them.  Take the written document with you when you meet with the principal and ask them to review the situation.  Ask the principal what the school's anti-bullying policy is and what action the school will be taking to remedy this problem.  
 
After meeting with the principal, if you feel that they are unwilling to take the necessary action to keep your child safe, take your concern to the next level which is typically the superintendant or school board.  
 
Boys Town National Hotline
1-800-448-3000