This study compared the cognitive control skills of male incarcerated adolescents (n = 44), male control adolescents (n = 33), male incarcerated young adults (n = 41), and male control young adults (n = 35) using the AX-continuous performance test (AX-CPT). This test measures proactive control (the ability to maintain a mental representation of goal-related information in preparation for a behavioral response) and reactive control (the ability to activate goal-related information in response to an external trigger). Incarcerated individuals had more difficulty implementing proactive control, whereas control individuals had more difficulty implementing reactive control. Adolescents had more difficulty with both reactive and proactive control compared with young adults, suggesting that both skills improve with age. Additional analyses indicated that the effect of age on proactive control was due to the presence of attention-deficit/hyperactivity disorder, whereas the effect of age on reactive control appeared to be a natural developmental trend that could not be explained by other variables. These findings are considered in relation to the dual mechanisms of control theory [Braver, T. S., Gray, J. R., & Burgess, G. C. (2007). "Explaining the many varieties of working memory variation: Dual mechanisms of cognitive control." In A. R. A. Conway, C. Jarrold, M. J. Kane, A. Miyake, & J. N. Towse (Eds.), "Variation in Working Memory." New York: Oxford University Press.]. (Contains 3 tables and 3 figures.)