There's been a lot of talk in education about the message from research that self-control in pre-schoolers predicts their later success in the classroom and in life. While I do think that this is an important message that should be taken on board by educators and parents, it's worth ameliorating it somewhat with the odd caveat - as offered in this latest study.
Simon Makin at Scientific American:
Celeste Kidd … suspected there might be a common misconception about the classic marshmallow study—namely, that waiting is always the right choice. While volunteering years ago at a homeless shelter for families in Santa Ana, Calif., she realized that all the kids around her would eat their marshmallows straight away, living as they did in an environment where anything they had could be taken away at any time. “Delaying gratification is only the rational choice if the child believes a second marshmallow is likely to be delivered,” Kidd says.
Although previous marshmallow-type studies have acknowledged that external factors might influence kids’ ability to wait for the bigger reward, none had directly tested for those factors’ effects.