A Tunnock's Tea Cake is seen in Edinburgh, Scotland May 2, 2014.
A Tunnock's Tea Cake is seen in Edinburgh, Scotland May 2, 2014. Started in 1890, Tunnock's is one of the oldest family firms in Scotland, their teacakes contain a puff marshmallow atop a biscuit covered in a layer of milk or dark chocolate. Reuters/Suzanne Plunkett

The famous marshmallow test may not be all that reliable. A new study has found that the delayed gratification test heavily favoured children from wealthy background and that it did not indicate real discrepancy in the kids’ success.

The findings, headed by researchers Tyler W Watts, Greg J Duncan and Haonan Quan, revisited the Stanford marshmallow experiment by psychologist Walter Mischel, which suggested that delayed gratification had huge benefits. The researchers were sceptical of the original results, which were based on experiments involving fewer than 90 children who were all enrolled in a preschool on Stanford’s campus.

In the original study, the children offered a marshmallow that they can consume immediately, but they were told that if they waited for approximately 15 minutes, during which the tester left the room and returned, they would be given another marshmallow or another reward, such as a cookie. Mischel found that the children who waited for 15 minutes became more successful in adulthood than those who didn’t.

But in the new test, Revisiting the Marshmallow Test: A Conceptual Replication Investigating Links Between Early Delay of Gratification and Later Outcomes, Watts and his colleagues found that the results of the original may have been skewed heavily in favour of the rich kids.

They used a much larger sample of more than 900 children, who came from different races, ethnicity and parents’ education and income. Their study involves the analysis of two variables: a child’s ability to delay gratification just before entering school and both adolescent achievement and socioemotional behaviours.

“Concentrating on children whose mothers had not completed college, we found that an additional minute waited at age 4 predicted a gain of approximately one tenth of a standard deviation in achievement at age 15. But this bivariate correlation was only half the size of those reported in the original studies and was reduced by two thirds in the presence of controls for family background, early cognitive ability, and the home environment,” according to the finding.

“Most of the variation in adolescent achievement came from being able to wait at least 20 s. Associations between delay time and measures of behavioural outcomes at age 15 were much smaller and rarely statistically significant.”

The researchers found that certain factors, including the children’s household income, might explain their ability to recognise delay gratification. Children from poorer families were more likely to eat the marshmallow immediately because they believed that if they waited, they would get nothing at all. This was because they were used to having only a certain amount of food at home, and it’s unlikely for them to get another treat.

Children from wealthy families, meanwhile, “passed” the marshmallow test because they had enough food at home. They had an easier time to wait for 15 minutes for extra treat.

The study concluded there was limited support for the idea that delay gratification leads to better outcomes. Instead, it suggested that a child’s social and economic background, is what’s behind their long-term success.