This article describes an investigation based on a corpus of original and redrafted versions of extracts from reflective narratives by 15-year-old secondary school students in the UK. It builds on the established research on sentence combining with respect to students' writing development. The findings are discussed in relation to the use of coordinating conjunctions, the subordinating conjunctions "as" and "because" and subordination other than explanatory "as" and "because". They suggest that aspects of grammatical development in students' writing are integrally related to propositional meaning, cohesion and rhetorical effects, and in particular that redrafting can enable students to explore forms of expression in their own writing, that coordination and use of explanatory "as" and "because" can enable students to explore relationships between clauses in writing, and that a complex process of rank shift of clause types, including subordinate clauses, can enable students to enhance their clause planning and their ability to elaborate.