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OBJECTIVES To examine the effects of a structured exercise program implemented during school break-time on working memory maintenance and neurophysiological indices of task preparation processes in adolescents. DESIGN Using class-wise random allocation, participants from four classes were divided into an exercise (n=20) and a wait-list control group (n=16). Over a period of eight weeks, the exercise group engaged in 20min of combined aerobic and coordinative exercise on each school day. METHODS Prior to and after the intervention period, participants performed a computer-based Sternberg task for the assessment of working memory performance. Simultaneously, the contingent negative variation (CNV) of event-related potentials was measured. RESULTS The exercise group demonstrated a larger decrease in reaction time from pre- to post-test relative to the control group, F(1, 31)=13.5, p<0.001. No changes were found for accuracy on the Sternberg task across groups. Using cluster-based permutation testing, the analysis of event-related potentials revealed a significant increase of the initial CNV from pre- to post-test in the exercise group, cluster value=-2376.2, p=0.006, which was most pronounced for the fronto-central region, with no such effect observed for the control group. CONCLUSIONS Daily engagement in a short combined aerobic and coordinative exercise program following the school lunch time break elicits benefits for working memory in adolescents. These changes are accompanied by improvements of task preparation processes, which allow the selection of a more appropriate cognitive control strategy.