The findings of the original study were called into question by a larger 2018 study[0]. The original study had 90 students. Some folks did a study with 900 people. They found the same correlation that the original study did. But when they controlled for household income, they found most of the correlation disappeared.
The obvious conclusion is that household income is a predictor of both:
- inability to delay gratification, and
- higher academic achievement
This makes sense when you consider that someone growing up in a poor household may have both:
- less reliable/continuous/predictable access to material things, meaning they would rationally seize immediate opportunities rather than taking the risk of a larger future opportunity, and
- less academic support
Now, this new study (OP) goes even further, finding that the correlation itself is weak.
[0] Watts, T. W., Duncan, G. J., & Quan, H. (2018). Revisiting the Marshmallow Test: A Conceptual Replication Investigating Links Between Early Delay of Gratification and Later Outcomes. Psychological Science, 29(7), 1159-1177. https://doi.org/10.1177/0956797618761661
The obvious conclusion is that household income is a predictor of both:
- inability to delay gratification, and
- higher academic achievement
This makes sense when you consider that someone growing up in a poor household may have both:
- less reliable/continuous/predictable access to material things, meaning they would rationally seize immediate opportunities rather than taking the risk of a larger future opportunity, and
- less academic support
Now, this new study (OP) goes even further, finding that the correlation itself is weak.
[0] Watts, T. W., Duncan, G. J., & Quan, H. (2018). Revisiting the Marshmallow Test: A Conceptual Replication Investigating Links Between Early Delay of Gratification and Later Outcomes. Psychological Science, 29(7), 1159-1177. https://doi.org/10.1177/0956797618761661