Aim: To promote the practice of physical activity (PA) after school hours and verify the effects on the physical fitness and academic performance of children with socioeconomic vulnerability. Methods: The non-randomized experimental study was carried out in a school in a vulnerable area. Eighteen children performed 60 minutes of moderate-vigorous PA and 15 minutes of circuit exercise (muscle and bone strengthening) three times a week. The control group (n=10) only had school physical education as a weekly PA routine. To assess the program's impact, physical aptitude tests (pre- and post-test) were carried out in accordance with the recommendations of PROESP-Br and the School Performance Test, which assesses learning in three categories: reading, writing, and arithmetic. Results: Abdominal strength, flexibility, sprint, and lower limb power increased (d-Cohen>0.20). Regarding academic performance, the effect was moderate (d-Cohen>0.50) for reading and total scores. The effect size was small (d-Cohen<0.50) for arithmetic and writing. Conclusion: An after-school PA program positively impacts physical fitness and academic performance in socioeconomically vulnerable children. The level of impact varies between small and medium according to different physical fitness capacities. School is an enabling environment for children to meet the World Health Organization PA recommendations.