Methodologies were proposed for combining background and aptitude and/or achievement information in an approach to the classification problem using the concept of under- and overachievement. The methodologies were applied to independent samples from four high school curricula. The results suggest that when past achievement and/or aptitudes were held constant (1) groups characterized by overachievement in all four curricula had similar backgrounds as defined by their level and pattern of responses to five biographical variables, (2) groups characterized by underachievement in the four curricula appeared to have similar response patterns but had more variation with respect to level and (3) underachieving groups regardless of curricular chioce reported that they spent more time on extracurricular technological projects than did overachieving groups. To a somewhat lesser extent underachievers tended to have fathers who discouraged their going on to college and they (the underachievers) also tended to spend more time on extracurricular reading. (Author)