Expository text writing is an essential skill for EFL primary school students, particularly where English is the medium of instruction. This quasi-experimental study examined the effects of explicit text structure instruction on the expository text writing of grade 7 EFL learners. Two intact groups of learners were randomly selected from two schools and designated as the experimental (n=44) and control (n=39) groups. The experimental group received explicit text structure instruction in two phases, while the control group followed the regular curriculum. Analysis of the post-test data using ANCOVA indicated that the experimental group significantly outperformed the control group in text structure identification (η2= 0.34), as well as in writing simple descriptive (η² = 0.28) and cause-and-effect paragraphs (η² = 0.37). An in-depth analysis of the participants’ writings showed that the experimental group included more main ideas/supportive details, and more precise word choices in their simple descriptive (η2=0.57 and η2=0.07) and cause-and-effect paragraphs (η2=0.43 and η2=0.35), respectively, with effect sizes ranging from medium to large. Moreover, the participants in the experimental group demonstrated significant improvements in their topic sentence writing quality, particularly in simple descriptive paragraphs (η² = 0.06), with a medium effect size. Finally, the study concludes with practical implications for EFL writing instruction and recommendations for future research.