The purpose of the study is to increase the level of flexibility in children 9-10 years old in physical education classes at school. Materials and methods: Quasi-experimental, non-randomized study. The pedagogical experiment was conducted based on the Ilyinskaya rural school in Russia from September 3 to December 27, 2022. The study involved students from the third grade in the number of 36 people. Children from the control group were engaged in the usual physical education program at school, and children from the experimental group, after a short running warm-up, performed a set of exercises to develop flexibility. To determine the flexibility indicators, control standards from the physical education program at school were used sit and reach tests, lateral spagat and shoulder rotation test with cane. Results. After the study, the indicators of children from the experimental group showed a significant increase in all 3 tests. The indicators of flexibility in the "Sit down and reach" test increased by 36.4% (p<0.05), the indicators of the "Lateral spagat" test increased from 12.5±2.1 to 8.9±1.9 (p<0.05), and the data of the "Shoulder rotation test" test increased by 18.7% (p<0.05). The children in the control group also improved, but not significantly, on all three tests. The indicators in the "Sit down and stretch" test decreased by 7.4% (p>0.05), the indicators in the "Lateral spagat" test decreased from 12.8±1.8 to 11.7±2.0 (p>0.05), and the data in the "Shoulder rotation test" test changed for the better by 9.9% (>0.05). Conclusion. If used a set of exercises to develop flexibility in physical education classes at school when working with children 9-10 years old, then their indicators will significantly improve joint mobility, passive flexibility, active flexibility, schoolchildren, physical culture, sensitive periods. Keywords: Physical Fitness; Motor Skills; Range of Motion, Articular; Child.