At least four people are affected by materialism in the story. The first is obviously Hester, the mother. It is her constant concern about money that is the motivation for Paul to find a way to please her. However, he could not have won so much money without the help of Bassett, the gardener or Uncle Oscar. Bassett helps Paul place bets and Oscar helps funnel the money to Hester. Finally, there is Paul himself, who want so much to " help"his mother than he ignores his own health and eventually dies in the pursuit of "a winner". Bu implication, Paul's father also had to be affected but he seems not to notice what is going on. A sentimental writer might have ended the story with Paul picking the winner of the Derby, living to see his mother happy with 80,000 pounds and living happily ever after. However, the author's point was to point out the dangers of a materialistic mother and a sensitive son who was willing to do anything for her.
Hester, Paul's mother is affected by materialism because she is obsessed with money and is unable to show any kind of love toward her son. Paul's uncle, Oscar Creswell is also affected by materialism. When Creswell finds out about Paul's ability to pick winners of horse races, he uses this to increase his wealth. He doesn't really care about the affects that it has on Paul until Paul dies. Paul is affected by materialism the most. He realizes that his mother isn't happy, so he does everything in his power to make more money, which ultimately leads to his death.
A sentimental writer might have ended the story by having Paul recover after his big win and have Hester realize the that her son is more important than money. However, by not ending the story with a "happily ever after" moment, the reader is more strongly affected by the lesson.