Bear in mind that you may not hear about it. Most children do not tell their parents, even when they are being severely bullied. (They are ashamed or feel their parents cannot help.)
Hence, keep in touch with your child on school matters, so that he or she will share what is happening - in the belief that you can and will help.
Don't even suggest that your child is weak and should be able to stand up to the bullying. Neither suggest that you will 'take care of it.' Discuss what has been happening calmly and explore possible options.
Don't try to sort out the problem with the parent(s) of the perpetrator. Almost always this approach makes matters worse.
If your plans - with the child - do not work, seek help from the school. But don't abuse the school for failing to keep your child safe. Give the school time to investigate - and (most important!) see that they get back to you.
If the school fails to help - and the bullying continues, explore options, such as informing the administrative jurisdiction or department responsible for the school. If you decide to take the child away from the school make your decision known to the school and the relevant school bodies.