"The study from Western Cape primary classrooms reports on how language is used in teaching and learning of natural science in the intermediate phase (Grades 4-6). The focus is on the way in which isiXhosa, learners' home language, is used alongside English (the resource language and medium of teaching and learning) in mediating cognitively challenging subject content, particularly natural science concepts and terminology. To this end, classroom observations and interviews with teachers were done, and teaching and learning materials such as textbooks and learners' work were explored. The study concludes that the lack of materials in sisXhosa, coupled with unplanned code switching to English and the extensive use of English borrowings, affect learners' ability to understand cognitively challenging material"--P. 4 of cover.