In an increasingly diverse society, young children are likely to speak different first languages that are not the majority language of society. Preschool might be one of the first and few environments where they experience the majority language. The present study investigated how preschool teachers communicate with monolingual English preschoolers and preschoolers learning English as an additional language (EAL). We recorded and transcribed four hours of naturalistic preschool classroom activities and observed whether and how preschool teachers tailored their speech to children of different language proficiency levels and linguistic backgrounds (monolingual English: n = 13; EAL: n = 10), using a suite of tools for analysing quantity and quality of speech. We found that teachers used more diverse vocabulary and more complex syntax with the monolingual children and children who were more proficient in English, showing sensitivity to individual children’s language capabilities and adapting their language use accordingly.