Should they be teaching racism at school??

[Smoke Jaguar]

I think you already agree with the last post about changing schools
I don't think this school gels with your values at all, apart from the umbrella interest in teaching in an Islamic environment.
I also think your DS would get a far more impartial view of the world even in a Catholic school, where I found going to school with kids from other religious backgrounds to be of great benefit to both parties (ETA: should probably mention that I wasn't Catholic, either!).
I don't think they're committed to teaching acceptance. Real concern would have seen some sort of satisfactory show of action well before now, instead of reaction by moving the teacher onto other students
Your DS is pretty special - the other kids will have absorbed this information and adopted it as their own, and your son has questioned it...this bodes well! Yes, it may make a long-term impression on him, and I am thinking that it will be one that keeps reminding him of why NOT to think that way because it has violated his own logic.
This reflects on you, too. What is demonstrated and modelled in the home at this age is a lot more powerful than what a teacher or curriculum can impart. For the other kids to take this away and not question it means they're not getting a lot of a different message at home, which is a real shame and happens in all walks of life about all sorts of values.
I don't think that teaching kids about 'difference' helps, and I think that kids that age CAN learn about how people use 'difference' to keep themselves above someone else, even if it means making up a difference, or making a kind of difference mean something more than what it is. In the case of Blue Eyes/Brown Eyes (classic social psych undergrad stuff!) a 'difference' such a eye colour meant nothing significant before it was MADE to be significant for the experiment's aims. What actually made no difference before suddenly did. Kids DO grasp these concepts and it's how the the perceived difference is manipulated we need to be making kids aware of, and why it's 'bad', rather than saying "well, discrimination is when this group doesn't like this group", which then acts to naturalise the discrimination as if it's a 'natural reaction' to difference. Kids need to learn there's nothing 'natural' about it and it's learned and encouraged, depending on which side of privilege you are sitting on!
Sorry, my Honours thesis was about racism, and though I've grown up being the quintessential 'different' person (of mixed cultural background - I refuse to use the term 'race' because it has no real meaning, though the myths about it create racisms) in just about every situation (including either of my parents' original countries!), my thesis challenged me in what I thought I knew about discrimination, racism, difference and how young these ideas are instilled in us. It's never too early to erode ideas of perceived difference! My DS, when referring to me in third person, still says 'him' - most kids his age have been taught already to staunchly identify their gender, and though he'll learn to do this eventually (I suppose!), the delayed perceived importance of gender is quite ok with me! Slightly OT, but related

[SallyJ]

I think you already agree with the last post about changing schools
I don't think this school gels with your values at all, apart from the umbrella interest in teaching in an Islamic environment.
I also think your DS would get a far more impartial view of the world even in a Catholic school, where I found going to school with kids from other religious backgrounds to be of great benefit to both parties (ETA: should probably mention that I wasn't Catholic, either!).

The most impartial view of the world you will get is in a public school, all religious schools have some kind of link (and I have taught in catholic and anglican schools as well as public schools). The curriculum is the same no matter what kind of school you attend.