Well, at first it was 'the kids who wait will later in love do better, see they have patience' but latest research IIRC (And I maybe wrong) says that actually, the test didn't take into account which kids wer middle class and up anyway. The ones who came from more affluent families were willing to wait, perhaps because they didn't worry about never having this sort of chance again. The less well off? Those kids had more reason to take the chance while they could as promises of future rewards were in their lives unreliable