Oh Dave, you're so right there! As a primary school teacher, I saw this so often. I think I related on here a while ago about the white South African lad of about eight who arrived in my class. There was an empty seat next to Ahmed, but the lad objected loudly (strong SA accent) "Ai daont sit nixt to BLEX!!" I was rather proud that my entire class gasped in horror. I took the boy outside and explained gently about 'all humans being the same, and we don't say those things here'. He hung his head and sat nixt to the bleck!
That summer, I shed a quiet tear when the same lad appeared with Ahmed in the three-legged race, arms about eachother. They'd become firm friends! (And they won the race too!)