I feel that the book also refers to the prejudices people had (and some people still have) against homosexuals. It becomes clear towards the end of the book that Michael, Billy's best friend, is homosexual, and throughout the book, there are different situations which support this. For example, one time when Billy goes to his friend's house, Michael opens the door fully dressed in his mother's clothes and makeup. Also, when the story is told through Michael's eyes, he actually states that he fancies Billy.
The word "poof" is used as an abusive word throughout the book, a word which is slang for homosexual. The prejudices against homosexuals also become clear when Billy's dad and brother discover that Billy takes ballet lessons, and they're frightened he might be a "poof".
This is my contribution to the post about the setting/social environment of the book. It will be edited before I use it in my analysis, and please bombard me with all the constructive comments you can think of! (I won't get offended.., don't worry).