In the absence of any kind of protection from the adults who are responsible for your child’s safety/well-being while at school, the only thing YOU can do is teach your child how to protect himself. Sign your child up for self-defense classes. Whichever type you find suitable/acceptable based on your beliefs and holds your child’s interest. There are all different types and styles. I make no recommendation either way.
There was a time here in the US when bullying was just part of growing up for some kids, and the schools did little, if anything, about it. In fact I think most people used to just think it was part of growing up. Here’s a question (Teaching children how to fight back) and a bunch of answers/comments that you might find interesting, if you have not already read it. The advice that OP was given was probably relevant (I neither support nor condemn) in an environment without rules or specific policies against bullying, which now is uncommon, at least here in the US. While it’s never easy to deal with a bully (as a parent of either a bully or a victim!) it is relatively easy to find advice about how to deal with bullies in a “zero tolerance” environment. Unfortunately, that’s not an option for you.
The harsh truth is sometimes these policies (depending on their application etc.) don’t work anyway, so it’s up to us, as parents, to give our kids the skills they need to get themselves out of a bad situation in one piece. Besides, bullying can happen outside of school; not so much while our children are so young they are always accompanied by an adult, but when they get older and start going off on their own to practices for sports or birthday parties, dances, etc. The adult to child ratio changes as kids get older so they need to learn to look after themselves.
I took martial arts as a young girl. I started taking karate (no idea what type!) classes just for fun, not to learn self defense per se. I have also attended various “self-defense” workshops sponsored by my university and employers. They each used different techniques and had different names, but they all had a similar goal: get out alive, as unharmed as possible, and do the least damage. (For example; Only use deadly force against deadly force because you’re not the jerk here, and/or because you don’t want to go to jail!)
While I certainly don’t often find myself in sketchy situations, the knowledge I have (I am certainly not “well trained” or anything) has served me well as I have had a few incidents over the course of my life where it came in handy. Not only does self defense training provide the skills to come out of a physical situation relatively unharmed, it also gives confidence in strength and ability, which in itself is a bully-deterrent. (Bullies thrive on power.) And if that isn’t enough, it also teaches you to spot aggression and avoid it, to diffuse/deflect, and to use the appropriate amount of force required in a given situation (don’t bring a gun to a knife-fight, in other words.)
I speak from personal experience on this topic. Yes, that means I was bullied and that on one occasion I ended up getting into a fight, after all attempts to avoid and diffuse/deflect failed. I didn’t start the fight, the verbal part or the physical part, and I didn’t “win”, but no real damage was done and the person who took it to that level never bothered me again. I had endured bullying for weeks. I was given all the usual advice: “Ignore him,” “tell a teacher,” “avoid him,” “tell him to go away/leave you alone,” “don’t get caught alone,” etc. As your child is experiencing, these things are sometimes not enough, but, I do believe it should be the first thing to try.
In my case, nothing worked, and it just escalated from taunting to theft to vandalism until finally assault and battery. The reprimands of teachers and principals only made it worse-he became more vindictive and saw my attempts to get help as further evidence of my weakness. This happened at school; one with “anti-bullying” policies that were basically ineffective against someone who just didn’t care about rules. Which is most bullies, or anyone who truly desires to cause harm.
There are some individuals in this world who lack social mores, self control, etc, so that their behavior/actions/intent is unpredictable and/or dangerous. No rule will provide protection against people like this, only avoidance or self-defense. It’s awful your son has to learn this lesson at age 8, but it’s the truth. I’m not saying his classmates are total sociopathic deviants, but, they definitely aren’t nice. Since avoidance doesn’t seem to be possible or effective, the only thing left is for your son to “fight back”, even if just enough to prevent further harm.
I think some of the other advice here (on this site, and in the previous answer) is good, particularly getting other parents to help out. (Maybe just so you can set up play dates so your kid has a “group” of his own and isn’t alone on the playground, getting singled out?) Ultimately, it’s not going to be one thing that fixes this situation for your child. It would be nice if the school would help out more, but since they can’t or won’t, and you can’t follow your kid around shielding him from jerks, the one thing you CAN do is teach your kid how to block a punch.