Here you go: https://pubmed.ncbi.nlm.nih.gov/2614657/ https://pubmed.ncbi.nlm.nih.gov/2614657/ > Delay behavior in both sexes was also correlated positively wi

Here you go: https://pubmed.ncbi.nlm.nih.gov/2614657/ https://pubmed.ncbi.nlm.nih.gov/2614657/ > Delay behavior in both sexes was also correlated positively with IQ and with Q-sort-derived indexes of ego resiliency and ego control. The relationship between ego control and delay behavior was particularly strong after both IQ and ego resiliency were partialled. These results were interpreted as reflecting the fundamental importance of both cognitive skillfulness and impulse control for adaptive delay behavior in situations that contain strong motivational inducements. This study doesn’t measure academic related delayed gratification. I’m surprised to be asked for a source. This has been settled science for decades.