The authors describe a series of experiments that explore 3 major ability determinants of individual differences in skill acquisition in the context of prior theory (e.g., P.L. Ackerman, 1988) and subsequent empirical and theoretical research. Experiment 1 assessed the predictability of individual differences in asymptotic skill levels on the Kanfer-Ackerman Air Traffic Controller (ATC) task. Experiment 2 provided an exploration of the construct space underlying perceptual-speed abilities. Experiment 3 concerned an evaluation of theoretical predictions for individual differences in performance over skill development in a complex air traffic control simulation task (TRACON) and the ATC task, with an extensive battery of general and perceptual-speed measures, along with a newly developed PC-based suite of psychomotor ability measures. Evidence addressing the predictability of individual differences in performance at early, intermediate, and asymptotic levels of practice is presented.