Recent theorising has suggested that expressive writing has greater potential to promote the growth of knowledge and understanding than does formal recordkeeping; and that students will develop a more formal style, in terms of discourse organisation and syntax, as they write repeatedly in a first- draft, close-to-speech style. There were, therefore, two studies in this project. The purpose of the first study was to explore the linguistic and learning development in Year 5 (10-11 years of age) students' expressive (that is, first- draft, close-to- speech) writing about classroom science activities over the duration of a six- week unit of science instruction. The purpose of the second study was to compare the effects of formal recordkeeping on students' science learning with the effects of expressive writing. Results revealed that the students' expressive writing changed significantly, on all indicators, toward a more formal, scientific style. Equally significantly, those students who engaged in expressive writing following the science activities performed better on tests of scientific knowledge and understanding than did students who wrote as directed by the teacher. However, contrary to expectations, there were no significant linguistic differences on the posttest explanations between the students who received instruction in how to write about the science activities and those who did not.