Which statement about The Stanford marshmallow experiment is incorrect? In this study, a child was offered a choice between one small but immediate reward, or two small rewards if they waited for a period of time. It's set of studies on delayed gratification in 1972 led by psychologist Walter Mischel Marshmallow studies never utilized longitudinal data. Researchers found, in follow up studies unexpected correlations between the ability to delay gratification and the success of the children many years later