The purposes of this study were (1) to identify and compare the effect on student achievement of an individualized computer-managed geometry course, built on behavioral objectives, with traditional instructional methods; and (2) to identify how selected individual aptitudes interact with the two instructional modes. The subjects were eleventh-grade students who elected geometry in their program of studies. The Cooperative Mathematics Test for Geometry was used to assess achievement, and scores from the Lorge-Thorndike Intelligence Tests, Tests of Academic Progress, and other selected variables were obtained. Analysis by a variety of statistical techniques indicated that the computer instruction curriculum and the traditional curriculum are equally effective in the development of skills in geometry and equally effective in producing achievement gains. The traditional curriculum is slightly superior in teaching nonverbal concepts related to geometry while the computer instruction is more effective in teaching verbal concepts. The L-T nonverbal scores and the final grades assigned in Algebra II are significant (.05 level) prediction variables on the Cooperative Mathematics Test. Students who study the computer are more likely to achieve at predicted levels of expectancy than students who study the traditional curriculum; the reverse is true for high-ability students. (Author/JP)