Cognitive flexibility refers to the ability to rapidly and accurately switch between tasks. It is regarded as a core dimension of executive functions and has been reported to improve during childhood and into early adulthood. For its evaluation, the task-switching paradigm is widely used. Switching between tasks or response sets imposes a series of costs on performance (i.e., mixing costs, global switch costs, local switch costs). There is less evidence analyzing switching performance in children than in other age groups, and few studies have specifically analyzed switching costs only in school-age children. In the present study, we aimed to analyze age-related changes in task switching in children aged 9-12 years old. We considered year-to-year changes in performance, specifically in response time based mixing costs, global switch costs, and local switch costs. To do this, we used a task switching measure to evaluate 231 children in Argentina, aged 9-12 years (M age = 10.94, SD = 0.88) who were aggregated into four age groups (9, 10, 11, and 12 years old). Results show consistent mixing costs, global switch costs, and local switch costs at each age. However, we did not find age-related differences in the magnitude of such costs. These results suggest that both the ability to maintain and select between two tasks, and to switch from one response set to another could be considered relatively constant during this period.