Low back pain (LBP) prevalence in children and adolescents is high during their lives. School-based interventions have reported effectiveness on back health. The study aimed to determine the effect of an educational back-health intervention on knowledge, postural habits and trunk muscle endurance regarding low back pain prevention for a group of 12 to 13-yearold students using a 6-month follow-up. A non-randomized experimental design. Three groups of 1st-grade secondary school students were selected. A control group (CG), and two experimental groups (EG1 and EG2) who participated in a back-health educational program (BHEP); only one of the experimental groups was given a follow-up learning contract (EG2). Assessments were performed at three different time points: before the intervention (baseline), after (post-test) and 6 months after (follow-up). The level of general knowledge of the experimental groups improved after the intervention. The level of postural habits improved in EG1 and EG2 compared to the CG after the follow-up period (p < .001 in both). A lower percentage of problems in the lumbar area in EG2 was observed after the 6-month follow-up. Teaching students to take care of their spines seems to have positive effects concerning knowledge, postural habits, and back health.