Well this whole thing made me think back to my childhood (which was a long time ago admittedly).
When I was 14 I was at a comprehensive in Leicester, which has always been a very ethnically diverse city. My recollection is that casual racism, most often in the form of “jokes” was pretty widespread, although it was also solidly opposed through school policy.
I can remember sniggering when one of my classmates spontaneously went into a Bruce Lee impression in front of a Chinese classmate (although I think I mainly sniggered at the fact that he got a hefty punch in the face for doing it). In one English lesson I recall being bored and deciding to write every racist joke I could recall on the back of my exercise book. I have no idea why I did it, but I did realise it was a stupid thing to do pretty quickly, binned the book and never did anything like that again.
In summary I think 14 is still plenty young enough to be experimenting with the ideas of right and wrong. My (nearly) 14 year old niece posted a picture of her feet up on a footstool on Facebook the other day, but I don’t really have the heart to tell her that she’s a terrible cliché.