A large sample study (n = 513) was conducted to investigate executive control performance in pupils following an immersion education program. We recruited 10-year-old children (n=128) and 16-year-old adolescents (n=127) who were enrolled in English or Dutch immersion education in French-speaking Belgium for at least 4 school years. They were com- pared to non-immersed children (n = 102) and adolescents (n = 156) on a number of execu- tive control tasks assessing inhibitory control, monitoring, switching and attentional abilities. Several control variables such as receptive vocabulary, nonverbal intelligence, socioeconomic status and other potentially relevant background variables were also considered. Our results show significant gains in foreign-language proficiency for the immersed compared to the non-immersed participants. These gains were however not associated with any measurable benefits on executive control. Our findings make a unique contribution to understanding how language and cognition develop through formal education methods that promote bilingualism.