Replication crisis, episode 1382:

This new paper found that among kids whose mothers had a college degree, those who waited for a second marshmallow did no better in the long run—in terms of standardized test scores and mothers’ reports of their children’s behavior—than those who dug right in. Similarly, among kids whose mothers did not have college degrees, those who waited did no better than those who gave in to temptation, once other factors like household income and the child’s home environment at age 3 (evaluated according to a standard research measure that notes, for instance, the number of books that researchers observed in the home and how responsive mothers were to their children in the researchers’ presence) were taken into account. For those kids, self-control alone couldn’t overcome economic and social disadvantages.

https://www.theatlantic.com/family/archive/2018/06/marshmallow-test/561779/