Learning to write paragraphs and thus learning how to sub-divide a text for topical and organisational coherence is an accepted part of acquiring writing maturity, and most teachers of writing will include explicit teaching of paragraphing techniques within their writing instruction classes. However, there is relatively little pedagogical or empirical attention devoted to understanding the nature of development in paragraphing — how writers increase in sophistication in managing paragraphs, and the pathways of development from not using paragraphs to secure mastery. The study reported here, therefore, set out to answer the research question — what developmental trajectories are evident in mastering paragraphing in secondary-aged writers? The article draws on a detailed linguistic analysis of a corpus of writing samples from 359 students stratified by age (13 or 15) and gender and posits a model of development in which the trajectory is from graphical organisation through to topical organisation and finally to textual organisation. However, the trajectory is not simply linear as the demands of longer, more complex texts create new challenges in paragraph organisation for able writers.