Background: Some health problems can be associated with the school environment and lifestyles, so it is necessary to carry out intervention actions that promote health and problem prevention. This study evaluates the effects of a Back School and Postural Education on improving short-term and long-term ergonomic knowledge of postures adopted at school and home, as well as reducing low back pain (LBP) in adolescents. Methods: The sample comprises 98 students, aged 10–16 years (11.61 ± 1.28 years), with 63 (64.3%) girls. The measuring instruments included a theoretical and a practical test, a low back pain (LBP) questionnaire and a scale. The tests and the scale have been applied 1 week before the intervention, 1 week following the Back School and Postural Education Program, and a 1 year later. The questionnaire was applied 1 week before of intervention and after 1 year. The intervention included three sessions of a theoretical and practical nature, each lasting 45 min, with intervals of 1 week. Results: The values of the theoretical test before the intervention, 1 week, and 1 year after the intervention were, respectively, 8.67 ± 2.64, 11.37 ± 1.93, and 11.11 ± 1.92 (p ≤ 0.001), and the practical test were 6.42 ± 2.47, 12.48 ± 2.25, and 12.83 ± 1.78 (p ≤ 0.001). The presence of LBP fell by 42.9%–25.5% after the 1-year period. Conclusions: Our data show an improvement of ergonomic knowledge of postures adopted at school and home as a result of the education program and a decrease of self-reported LBP.