Okay, thank you everyone for responding.

I've more or less decided to go ahead with homeschooling and am currently in contact with school authorities who will provide me with necessary supplies and information once I get back to Oslo.

Master of none, you're quite right and thanks for saying it even if it seemed obvious.
I just can't possibly risk lasting psychological harm to my child and have therefore decided to pull him out of school. I want him to grow up in an environment where he feels safe and develops faith in himself, rather than worthless.
The trip to Bergen has been good for us and although he still hasn't opened up fully, I've heard enough to decide that school isn't providing the supportive environment that I want.

It was a big decision to take and not easy at all but now that I've taken it, I feel happy that at the very least, the bullying will definitively stop.

Thanks once again, everyone for your inputs and encouragement! I couldn't have taken the decision without you.