This study of three science teachers' lessons on heat and temperature seeks to characterise classroom talk that highlighted the ways language is used and to examine the nature of the language demands revealed in constructing, negotiating, arguing and communicating science ideas. The transcripts from the entire instructional units for these teachers' four culturally and linguistically diverse Grade 4 classes (10 years old) with English as the language of instruction constitute the data for this investigation. Analysis of these transcripts focused on teachers' talk that made explicit reference to the form or function of the language of science and led to the inductive development of the "Attending to Language Demands in Science" analytical framework. This framework in turn revealed that the major foregrounding purposes of teachers' talk include labelling, explaining, differentiating, selecting and constructing. Further classification of the instances within these categories revealed the extensive and contextualised nature of the language demands. The results challenge the conventional assumption that basic literacy skills dominate over disciplinary literacy skills in primary school science. Potential uses of the analytical framework that could further expand our understanding of the forms, functions and demands of language used in elementary school science are also discussed.