In the first four chapters of A Separate Peace by John Knowles, does affluence play a part in shaping the boys' attitudes?
This is an interesting question, because the idea of money or affluence is never really mentioned in A Separate Peace, by John Knowles. It is true that Devon is a boarding school and, presumably, the boys who attend it come from families with some financial means; however, that assumption may or may not be true due to the wartime economy, as discussed in more detail below. You do not mention any specific attitudes in your question, but in general the boys' attitudes at Devon do not seem to be shaped by their assumed affluence.
The older boys at this elite school are doing what every other boy across America is doing--if they are old enough, they are preparing for war. The younger boys, sixteen-year-olds such as Finny and Gene, are a bit more removed from the preparations. Gene says:
We were registered with no draft board, we had taken no physical examinations. No one had ever tested us for hernia or color blindness. Trick knees and punctured eardrums were minor complaints and not yet disabilities which would separate a few from the fate of the rest. We were careless and wild, and I suppose we could be thought of as a sign of the life the war was being fought to preserve. Anyway, they were more indulgent toward us than at any other time; they snapped at the heels of the seniors, driving and molding and arming them for the war. They noticed our games tolerantly. We reminded them of what peace was like, of lives which were not bound up with destruction.
There is no expectation that, just because they come from affluent families, these boys will be exempt from doing their duties. Their mischievous antics over the summer session are not because they are rich and entitled and think they can get away with it; it is because the rules at Devon are more lax during the summer session.
In fact, in chapter three Gene remembers the war years, and money provides very little power or influence for any American:
America is not, never has been, and never will be what the songs and poems call it, a land of plenty. Nylon, meat, gasoline, and steel are rare. There are too many jobs and not enough workers. Money is very easy to earn but rather hard to spend, because there isn’t very much to buy.... To waste anything in America is immoral. String and tinfoil are treasures.... All pleasurable things, all travel and sports and entertainment and good food and fine clothes, are in the very shortest supply, always were and always will be. There are just tiny fragments of pleasure and luxury in the world, and there is something unpatriotic about enjoying them. All foreign lands are inaccessible except to servicemen; they are vague, distant, and sealed off as though behind a curtain of plastic. The prevailing color of life in America is a dull, dark green called olive drab. That color is always respectable and always important. Most other colors risk being unpatriotic.
It certainly does not sound as if Gene and his friends see the world any differently than people who might be less affluent, and they are certainly not assuming their position in society or their money (if they do, indeed, have such things) will buy them any kind of preferential treatment. Given that, it does not seem as if affluence shapes anything special in the actions or attitudes of the boys at Devon.