Although many studies modelled writing quality by analysing basic skills (spelling, grammar, etc.), few focused on top-down compositional strategies at the discourse level. We propose that using both narrative and argument discourse modes in an argumentative essay (a multi-discourse mode [MDM] strategy) capitalizes on their complementary advantages, yielding higher quality argumentative essays. We tested whether MDM strategy and linguistic features were linked to essay scores in 695 Chinese high-stakes exam essays by upper secondary school students. Path analyses showed that essays with the MDM strategy had higher scores. MDM essays also featured more words, shorter sentences, more infrequent words, and more concrete words--all contributing to higher essay scores. Additionally, essays written from a picture prompt (versus a text prompt) had higher scores. This study captures how discourse strategies can improve essay writing.