Considerable research has addressed whether various academic factors affect involvement in delinquent behavior among youth. Yet few studies have assessed the association between academic underachievement and delinquency. Academic underachievement is defined as school performance, such as measured by grades, that falls below what is predicted by standardized tests of mental/cognitive ability. Using two waves of longitudinal data (n = 11,223), this study aimed to evaluate this association and determine if it is affected by school attachment, family relations, parental education, or self-control. The results of the empirical model suggested a modest association between academic underachievement and delinquent behavior, but it was partially attenuated by attention deficits, an indicator of low self-control. Additional analyses indicated that attention deficits were associated with both underachievement and delinquent behavior.