The main purpose of the present study was to investigate the importance of task persistence in young adolescence for successful educational and occupational attainment in middle adulthood. Data from age 13 (N = 1,092) and adult age (age 43 for women, N = 569 and age 47 for men, N = 393) were taken from the Swedish longitudinal research program entitled "Individual Development and Adaptation." In line with previous research, task persistence was found to be related to changes in grades between age 13 and age 16, over and above other childhood factors. Task persistence at age 13 was also a significant predictor of both income and occupational level in middle adulthood for the men, controlling for a number of childhood factors (including intelligence), and even when educational attainment in adulthood was taken into account. Finally, task persistence was related to educational attainment in adulthood. The authors suggest that task persistence is a second fundamental factor besides general mental ability, influencing attainment within the area of working life and education. The influence of task persistence is discussed in form of personality-environment selection mechanisms. (Contains 4 tables.)