In this study, the role of need for cognition, achievement motivation, and conscientiousness on academic underachievement was investigated. Forty-seven male and 46 female students in Grades 7 to 10 participated in the study. Student attributes were assessed by self-report measures, school performance by academic grades, and intellectual abilities by a standardized structure of intelligence test. A regression analytic model (prediction of grade point average by general intelligence) was used to operationally define underachievement. A categorical cutoff definition as well as a continuous definition was investigated. All relationships between underachievement scores and need for cognition, achievement motivation scales, and conscientiousness showed linearity. This warranted the use of a continuous definition of underachievement. Results revealed that need for cognition as well as facilitating anxiety contributed the most to the explanation of underachievement. © 2006 Wiley Periodicals, Inc. Psychol Schs 43: 401–411, 2006.