Evaluating the language of different types of explanations in junior high school science texts

Since 'it is written texts - and the talk around them - that provide the di scursive means for the development of the 'higher mental functions' (Wells 1994), the quality of writing and explicit use of texts in teaching warrant close attention. This is not to diminish the importance of 'hands on' inve stigations, observation and negotiation of understanding through talk. Howe ver, the complementary use of effective texts has a significant role. This article demonstrates how functional language analyses differentiate explana tion types and specify language features relevant to the effectiveness of t exts in apprenticing students to the language forms of scientific English. Key differences between different types of explanations are illustrated, th en sample text analyses show how language features index variation in expla nation quality. Implications are drawn for the selection and use of texts a nd the role of knowledge about language in teaching critical comprehension and composition of science explanations.