Don't Make Demands
You probably have ideas as to how the bullying can be stopped. Ask, though; don't tell. Demands like "Kick this student out of the school!" put teachers on the defensive. You are also insisting that they take actions beyond their pay grades. Don't waste your time, or their time, forcing them to explain why certain steps can't be taken. Instead, present your problem, and then ask them to help come up with solutions. As you gain allies, you can ask them to keep an eye out for your child, too.