Does he use the internet and are his parents aware of exactly what he is looking at online? Is he watching the news on tv - much of it is so worrying at the moment and they may be taking in more than you realise.
Bullying doesn't just happen at secondary school - primary school children can be very unkind too, especially if they sense that someone is rather sensitive.
The school should be more aware of anything that may be happening - just suggesting different reading matter is not good enough.
in an intervention group, as I run in my school.
The DGC's primary school is quite pro-active too and something like that sounds like a positive way forward SisterAct