Now? Now somebody can capture things digitally using a pen. Yes, a pen! How about a watch? No, really! If the bullying is severe, I see NOTHING wrong with pinning a small recording device into a child's shirt or having them wear a spy camera watch and activate it while they're being bullied. That way, if the teacher claims they can't do anything because they didn't hear or see it, you can take the data off the device and email it to that teacher--or take a laptop into their office and let them see it off your laptop.
I remember a dad on youtube wiring up his son to catch teachers who were being cruel and they were brought to justice with the evidence. The same can work on peers who are bullies too.
In this day and age, it's a good investment.