I couldn't find Mischel's 1990 published findings anywhere online for free, but I did dig up this article which describes some of the data. http://74.125.95.13

I couldn't find Mischel's 1990 published findings anywhere online for free, but I did dig up this article which describes some of the data. http://74.125.95.132/search?q=cache:1ZRYswNI6dIJ:www.courseweb.uottawa.ca/epi6181/images/Delay_gratification.pdf+Predicting+adolescent+cognitive+and+self-regulatory+competencies+from+preschool+delay+of+gratification:+Identifying+diagnostic+conditions&cd=7&hl=en&ct=clnk&gl=us&client=firefox-a http://74.125.95.132/search?q=cache:1ZRYswNI6dIJ:www.coursew... In the follow up they looked at several factors: Scholastic Aptitude Test scores, sensitivity to rejection, overall functioning, educational attainment, drug use, ratings of self-esteem, and more. It looks like they checked the correlation of each factor separately. Besides experiment sample issues (which the linked document touches on) it looks the the experimenters were pretty rigorous in attaining valid results.