Background: Even though adolescents are engaged in physical activity during physical education (PE) classes, this does not guarantee that they experience intensity levels high enough to induce physiological adaptations, such as increasing cardiorespiratory fitness. Objective: This study aimed to compare the cardiorespiratory response to exercise, by analyzing the maximum oxygen consumption (VO2 max), the ventilatory anaerobic threshold (VAT) and the respiratory compensation point (RCP) parameters, of adolescent boys participating only in PE or in PE and school sports (SS). Methods: Twenty-five 14 to 15-year-old boys participated in the study. Students were divided into two groups whether they practice only PE (PE group; n=9) or PE and SS (PE+SS group; n=16). Weight, height, and percentage of body fat were measured. The cardiorespiratory response to exercise was analysed using a gas analyser and performed in a treadmill. The protocol consisted of constant and small increases in speed and slope. To identify ventilatory thresholds (VAT and RCP) combinations of visual and computerized criteria were used. Groups were compared using Students t-test. The significance level was set at p