BACKGROUND: A high prevalence of overweight/obesity among low socioeconomic status adolescents contributes to health inequalities. However, evidence-based interventions for reducing social inequalities in adolescent weight are lacking. We aimed to investigate whether strengthened care management for adolescents with low socioeconomic status has an equivalent effect in reducing overweight as standard care management in adolescents with high status.METHODS: PRALIMAP-INÈS was a multicentre trial including 35 state-run high and middle schools in the north-eastern France. A population-based sample of 1639 adolescents aged 13-18 years with screened and clinically confirmed overweight/obesity were proposed for inclusion and divided into two groups by the Family Affluence Scale score: advantaged (score > 5), receiving standard care management (A.S) and less-advantaged randomly assigned to two groups (1:2 ratio): standard care management (LA.S) and standard and strengthened care management (LA.S.S). Interventions were based on the proportionate universalism principle: universal standard care for all groups and proportionate care for the LA.S.S group. Main outcome was body mass index z-score (BMIz) assessed before and 1 year after inclusion.RESULTS: A total of 1419 adolescents were included and 1143 followed up at 1 year: 649 in A.S, 158 in LA.S and 336 in LA.S.S groups. BMIz decreased significantly for boys (-0.11 [95% CI, -0.13 to -0.08]; p < 0.0001) and girls (-0.05 [-0.08 to -0.03]; p < 0.0001). No equivalence between LA.S.S and A.S groups was evidenced. For girls, the trend to superiority for LA.S.S was confirmed by the more favourable change (-0.06 [-0.11 to -0.01]; p = 0.01) observed on superiority analysis, with no differential change for boys (0.02 [-0.03 to 0.08]; p = 0.41).CONCLUSIONS: A public health school-based intervention using the proportionate universalism principle may be effective in not worsening or even reducing overweight social inequalities in adolescents, especially for girls. Overcoming social barriers may help health professionals dealing with the burden and inequalities of overweight in adolescents.