"Self-Control Alone Couldn't Overcome Economic and Social Disadvantages"

"The failed replication of the marshmallow test does more than just debunk the earlier notion; it suggests other possible explanations for why poorer kids would be less motivated to wait for that second marshmallow. For them, daily life holds fewer guarantees: There might be food in the pantry today, but there might not be tomorrow, so there is a risk that comes with waiting. And even if their parents promise to buy more of a certain food, sometimes that promise gets broken out of financial necessity.
"Meanwhile, for kids who come from households headed by parents who are better educated and earn more money, it's typically easier to delay gratification: Experience tends to tell them that adults have the resources and financial stability to keep the pantry well stocked. And even if these children don't delay gratification, they can trust that things will all work out in the end—that even if they don't get the second marshmallow, they can probably count on their parents to take them out for ice cream instead."

Jessica McCrory Calarco at The Atlantic discusses "the class dimension of the marshmallow test."