This study investigated the utility of aptitude and learning rates for initial study units as predictors of time-to-mastery in an individualized, mastery-based course taught largely by TICCIT (Time-Shared, Interactive, Computer-Controlled Information Television) computer assisted instruction. A TICCIT student station includes a color television, a keyboard with specialized learner-control keys, and a light pen. Emphasis is on learner control over the instructional process. Subjects were 102 marines who graduated from the Communication Center Operator Course, which is designed to train students to work in communications centers throughout the Marine Corps. The Armed Services Vocational Aptitude Battery was utilized as an aptitude measure. Aptitude alone proved to be a weak predictor, accounting for only 12% of the variance in total time-to-mastery. By using both aptitude and initial unit learning times, 40% of the variance was explained. Results suggest that learning times over initial units may prove more useful than pre-course measures of aptitude in the prediction of time-to-mastery in individualized instruction. (Author/LMM)