I know that my question doesn’t have an easy answer but to not even feign an attempt via answering a question with a question is pretty telling.
No, it's not. It's an attempt to demonstrate that your question misses the point. I hoped that you would see that the answer to one was the same as the answer to the other. I hoped that you would find "how do you discipline a child stabbing another child in the eye?" more intuitive than "how do you discipline peer pressure?"
What you're actually asking is "how do you discipline a child?" What you're disciplining the child for is irrelevant. If you have undesirable behaviour, you apply the same methods and techniques.
You make sure that the rules and consequences are clear.
You have a set of gradated and well defined punishments.
You apply these with consistency and without malice.
You apply levels of punishment that are appropriate for the violation.
Ideally, you also reward positive behaviour, even if it's only as little as explicitly commending it.
My previous answer was an attempt to "teach" you by letting you think for yourself. As that hasn't worked, this time I've gone for an explicit explanation. I like this less, as I feel you're likely not to understand a simple list like this as well as if you'd had to think through it for yourself. You may disagree with my methods of discipline, for example, which are not universal and are just what I have found to work best.
But for your question, the method doesn't even really matter. If you have a method of disciplining children for
anything, you have a method that can be applied to peer pressure.
It should also be noted that adults can expect to be disciplined for certain types of anti-social behaviour, harassment and bullying. Teaching children that these boundaries exist and should be respected could be viewed as giving them a good foundation for entering the adult world. Instead of allowing an atmosphere in schools where extreme behaviour is tolerated, and expecting them to just switch that off when they enter the work force.
The issue goes a bit beyond just inter-child behaviour. Pressure to have high value clothing (or other) puts pressure on families that may not have the money to provide such accoutrements. There are often negative outcomes for families under that kind of pressure. That's one of the main reasons for school uniform in general.
Yeah, but I'm talking about things that we can actually control here. You can't do anything about some families being richer than others. School uniforms takes away one expression of wealth, but it really doesn't address the issue of kids bullying other kids over the wealth of their parents.
I find it preferable to address the core problematic behaviour rather than try and band aid it by regulating clothes, or hairstyles, or shoes, or pencil boxes. Rich people being visibly different to poor people is a real world adult thing. Teaching children how to deal with that appropriately seems like good life education.
I think that to many people schools have been reduced to a place to receive just academic education, times tables, literacy, etc. The reality is that this is a place where children spend a good proportion of their life, and is in many ways comparable to a workplace that they will experience as adults. Using that time in school to teach and prepare them for the life they are to lead as adults seems sensible to me, but I suspect that I'm a bit of an outlier.