Teachers' language practice during shared book reading may significantly affect the rate and outcome of early language proficiency. The current study has focused on 37 kindergarten teachers and 440 4-to 5-year-old kindergartners during their shared book reading sessions in Singapore, exploring teachers' variation in instructional strategies and linguistic features, and its relations with children's language development and teacher's background. Results demonstrated that teacher's language strategies and linguistic features varied considerably. Instructional strategies with a medium level of cognitive load were found to be positively related to children's growth in receptive vocabulary and word reading skills. Teacher's lexical sophistication was found to be positively associated with children's vocabulary size. Years of teaching experience was revealed to predict teacher's variation in medium-level instructions.