Delayed gratification reconsidered

There is an old psychological experiment where young kids get the choice between eating one marshmallows now or getting more of them later on. Those kids who resisted the temptation of instant gratification did later better at school and in their career. The article "You’re So Self-Controlling" put that in context. It depends to a large extent on expectations. If the kids know the time frame they are considerably more motivated to wait. If the experimenter has shown himself unreliable they are more likely to choose instant gratification. The article doesn't try to explain the original experiment in this context. My guess would be that the delaying kids had more reliable parents and that that helped them later in their life too.