I lent the book to my twelve-year-old sister, who's academically advanced but fairly sheltered (I had to get Mum's permission).

She damned it with faint praise but at least didn't seem traumatised... I'll make her read it again in a few years, and she'd darned well better appreciate it more! 'Yeah, it was alright' indeed! Philistine.
ETA: In case you haven't seen the film, it's very sensitively done, and not graphic or obscene at all. It maintains the child's POV of the book, so you don't see the rape or Tom getting shot. There are some slightly scary moments, and I wouldn't show it to
my ten-year-old sister, but only because she's easily creeped out.