Linguistic skills at the end of preschool are important known predictors of academic attainment throughout schooling. Moreover, research has shown that introducing children to a second language can serve as ameans of improving children’s linguistic skills. This practice is implemented in Greece, where children canattend ‘submersion’ preschools, where the curriculum is delivered in English, or ‘immersion’ preschools,where the curriculum combines the two languages such that some classes are in Greek and some in English.Nevertheless, little is known about the linguistic outcomes of the children who attend these programs and,thus, about the programs’ efficacy. The data reported in this paper stems from a (larger) study that involved140 preschool children between the ages of 4;10 and 5;11 (35 in submersion and 35 in immersion, alongside34 Greek monolingual and 36 English monolingual controls). The children participated in various tasks that included two standardized tests assessing their vocabulary and grammar in both Greek and English.Statistical analyses revealed that Greek-English emergent bilingual preschoolers received comparable scores on the vocabulary tests and higher scores on the grammar tests relative to their Greek monolingual peers.Notably, the immersion group outperformed the Greek monolingual group in all proficiency measures.These findings highlight that learning a second language at preschool does not hinder children’s linguistic development; rather, it benefits their first language skills, especially when the children’s two languages are equally supported. The findings suggest that English-medium programs, which are proliferating around the world, can give children the chance to achieve better linguistic outcomes and, by extension, greater academic success.