How does cognitive control change with age, and what are the processes underlying these changes? This question has been extensively studied using versions of the task-switching paradigm, which allow participants to actively prepare for the upcoming task (Kray, Eber, & Karbach, 2008). Little is known, however, about age-related changes in this ability across the life span when there is no opportunity to anticipate task goals. We examined the effect of 2 kinds of verbal self-instruction-labeling either the task goal or the relevant feature of the stimulus-on 2 components of cognitive control, goal setting and switching, in children, young adults, and older adults. All participants performed single-task blocks and mixed-task blocks (involving unpredictable switching between 2 tasks) in silent and labeling conditions. Participants categorized bidimensional stimuli either by picture or by color, depending on their spatial position in a 2-cell vertical grid. Response times revealed an inverted U shape in performance with age. These age differences were more pronounced for goal setting than for switching, thus generalizing results obtained in situations taping proactive control to this new context forcing reactive control. Further, differential age-related effects of verbalization were also obtained. Verbalizations were detrimental for young adults, beneficial for older adults, and had mixed effects in children. These differences are interpreted in terms of qualitative developmental changes in reactive goal-setting strategies. (PsycINFO Database Record (c) 2014 APA, all rights reserved).