Background: The aims were to: (1) examine the levels of physical activity (PA) during different time periods (ie, daily PA, school hour PA, recess PA, physical education classes [PEC] PA) in children and adolescents; and (2) identify the rate of compliance with the specific PA recommendations for these time periods. Methods: The participants were 1925 (940 girls) children and adolescents from 40 Spanish schools. Hip-worn accelerometers were used to assess PA during different time periods. Results: Boys and children were more physically active and had a greater percentage meeting the daily PA recommendation and the school-based PA recommendation than girls and adolescents, respectively. Compliance with daily PA recommendation was markedly higher than that with the school-based PA recommendation, regardless of sex and age groups (ie, 80.4% vs 24.1% for daily and school-based PA recommendations, respectively, in child boys). A very low percentage (ie, 9.7% and 1.2% of child boys with almost 50% of moderate-to-vigorous PA during recess and PEC, respectively) of students reached the recommended PA levels for recess and PEC. Conclusions: Physical activity levels during school hours, recess, and PEC in children and adolescents are very low. Promoting PA in school settings is essential, especially in girls and adolescents.