This longitudinal study examined the cognitive development of Spanish children from monolingual backgrounds attending schools with varying levels of English exposure (13%–83%) to assess whether higher L2 exposure results in advantages over time. 229 children (ages 6–7) completed background (nonverbal reasoning (NVR), working memory (WM), L1 vocabulary, L2 vocabulary) and experimental tests measuring attentional/executive functions (selective attention, divided attention, switching, inhibition) at the beginning and end of year 1 of primary education. Generalized linear mixed-effects models, accounting for factors such as family educational level, onset of L2 exposure and language exposure outside of school, indicated that children’s cognitive skills benefit from (high) L2 exposure at school, with greater L2 exposure being linked to more enhanced attentional/executive skills as well as to a larger L2 vocabulary. These findings support the positive effects of immersion programs, suggesting that L2 exposure in school settings alone can contribute to more developed attentional/executive skills.