How does the rocking horse winner portray the quest for material wealth?

In "The Rocking Horse Winner' by DH Lawrence, the family is not poor, but comfortably middle class. However, they crave riches and believe the only way this can be acquired is through luck. When the child displays a unique gift that allows him to pick the horses that will win in a race by riding his rocking horse and entering a trance like state, the quest for wealth takes a dark turn.