--- - |2+ Abstract Objective Although a growing body of research has confirmed the manifold advantages of being an optimist, only a limited body of previous research has addressed the antecedents of optimism in real‐life situations. This study examined whether parental socioeconomic status (SES), age‐salient experiences (i.e., doing well in school and perceiving acceptance from peers), and aspects of the student composition at school contribute to changes in the optimism of early adolescents. Method We followed a large sample of German seventh graders (N = 7,272; 52.9% females; baseline Mage = 14.1) at two measurement points over a period of 5 months and estimated latent regression models. Results First, optimism showed medium‐sized rank‐order stability between both measurement points. Second, parental SES predicted changes in optimism, but this effect was fully mediated by age‐salient experiences. Third, positive age‐salient experiences (i.e., academic achievement and perceived peer acceptance) predicted positive changes in early adolescents’ optimism. Fourth, our results suggested no effects of school peer composition. Conclusions The findings broaden our current knowledge about antecedents of changes in optimism during early adolescence by highlighting the effects of positive age‐salient experiences, namely, academic achievement and perceived acceptance from peers. - Journal of Personality, EarlyView.