Character and perception shaping for me when I first read it in sixth grade. I credit this book with instilling in me a prudent-yet-intense suspicion of anything 'utopian.' And that wasn't the only aspect I ultimately found formative. 
 It's funny... looking back, the minor (fantasy?) element of memory-transfer didn't strike me as anything fantastical. The imagery that came with those scenes became etched on my memory nearly as well as the ethical/societal quandaries this story presents. I'll cop to this being a critically impressionable age for me, but that makes the authorial accomplishment all the more significant. 
 Due to the content, I would not recommend it for children younger than 12, and advise parental participation in its exploration. But I also believe it to be too developmentally important to be missed out on.