Bullying sucks. It will surprise nobody that children who become the victim of bullying suffer — through research that clearly shows they feel stressed, angry, upset, worried, afraid, defenseless, alone, and even outright depressed exists , we don't really need studies to be able to establish that. What may come as somewhat of a shock, however, is that child victims of bullying are more likely to have poorer health, wealth, and social outcomes in adulthood .
While many kids don't tell their parents they are being bullied — some even because they're afraid their moms and dads will punish them or see them as weak  — research shows that most parents' dominant emotion, in learning their child has become the victim of bullying, is protectiveness . That feeling may turn out to be hard to translate into action, unfortunately. Like their children, parents of bully victims are likely to feel quite helpless as they seek to extract their sons and daughters from a difficult situation.
The Trouble With The Usual Advice
There's no shortage of articles about "what to do when my child is being bullied school" on the internet. As most parents entrust their child's education to public schools, which are in some way regulated by governments, I'm going to have a look at what two government-affiliated sources have to say about this. One is the Victoria State Government's Education and Training department (Australia) , and another a National Health Service Trust (UK) . I'd include the US' StopBullying.gov initiative, but though it has helpful content, it curiously doesn't feature specific tips on what to do when your child is being bullied. Understanding what makes a school bully and who is a vulnerable target for school bullying is a crucial part of the puzzle, but it doesn't do what you really want — to make the bullying stop.
So, the folks in Victoria want you to "take the bullying incident seriously and know that your child’s school will too." They also encourage you to stay calm and positive, and focus on finding a solution together with a child — which is good. They then go on to urge you to talk to the school. Tips they advise you to share with your child include, in brief:
- Telling the bully to stop.
- De-escalating the situation, "e.g. agreeing in an offhand way with the bullying when they say offensive or negative things".
- Talking to school staff about the bullying.
- Acting confident even when they don't feel it.
- Trying to "act unimpressed or unaffected".
The next tip for parents is not to advise their child to try to make the bullying stop by ignoring it (presumably not the same thing as acting unimpressed or unaffected?), fighting back, playing with a different group of friends, or bullying the bully, as these things won't work.
The NHS folks offer a different set of tips, beginning with recommending that you reassure your child that you will do everything you can not to make their situation worse for them, and that they were right to tell you about the bullying. They also encourage you to help your child make friends in places other than school to counter social isolation, which I appreciate as a former victim of bullying. Finally, they encourage the creation of a bullying log to detail incidents, and inform parents that all schools must have anti-bullying policies.
Research has identified a number of problems with the "rely on the school to fix the problem" approach, however:
- Parents may find that the school won't intervene as the teacher has not seen the bullying first-hand .
- Teachers may not intervene unless the bullying has become physical, as they do not see social exclusion as bullying .
- Anti-bullying policies may or may not actually be effective. 
- Even if your child's school takes your reports of bullying seriously, bureaucracy may get in the way. Parents report that it is often difficult to meet directly with teachers and principals, and you may deal primarily with a secretary who does not have the relevant details nor the power to make changes. 
- Schools may be reluctant to work together with you to improve your child's situation. 
The most common and obvious advice — to talk to the school — becomes useless if the school cannot, for whatever reason, help your child. If it can, brilliant. You can stop reading now. If you, too, have had (or are about to have) less-than-positive experiences with the way in which your child's school responds to complaints of bullying, another solution is clearly required.
So, What Does Make Bullying Stop?
A study of Swedish victims of bullying showed that one fourth of them gave "support from school personnel" as one of the reasons their bullying came to an end. Asking their peers for support, another strategy used, didn't always end the bullying, but did help break an unchallenged bullying culture among students by encouraging others to become upstanders rather than bystanders. Assertively engaging with bullies was another way in which some students successfully made the bullying come to a halt. Finally, moving schools or classrooms was as successful as relying on school personnel intervention. 
As a parent of a bullied child, this may give you some useful information, which you can also discuss with your child. In addition, I'll just throw the option of homeschooling out there. This educational option is on the rise, and it may be the right choice for some children who have been bullied.
You'll also want to step outside of the situation itself and take a look at how you usually solve problems. You've already identified the problem — the bullying — and the goal, which is to make the bullying stop and to see your child thrive socially and emotionally. How can that happen? Brainstorming solutions, considering their pros and cons, and then implementing your chosen option once you and your child have talked about it is the way to generally go about this.
Though your child needs to be included in this process, and the school might too, I'd caution against following either of their leads entirely. Your child may not want you to talk to their teacher, for instance, for fear that the bullying gets worse. Despite not feeling good at their existing school, they may also be reluctant to move to a new school. Take their opinions into consideration, but especially for younger children, don't feel you have to do what they see as best — you have a bit more experience under your belt. School staff, likewise, may suggest solutions as varied as ignoring the bully to changing the way your child dresses to better fit in. If it doesn't work, keep looking for solutions!
In the meantime, work on helping your child find new social outlets that don't include any of the people they currently interact with. From Scouts to swimming, from robotics clubs to mythology competitions, activities where your child can meet others who are passionate about their interests may open an entirely new window to friendships and confidence.