This study investigated whether students' writing achievements could increase using a modified roundtable technique based on the process approach and to find out what aspects of writing significantly increase. A quantitative study in the form of preexperimental design was conducted which involved 21 tenth grade students of a 1 Pekalongan-Lampung province senior high school 1 in Indonesia. The overall obtained pre- and post-test writing data were compared through the Paired sample t-test both in the overall sample and for each specific aspect. The results demonstrated that there was a significant increase in the students' writing achievements. The significant increases were found in all writing aspects, except mechanics. This modified roundtable technique makes learning situations enjoyable and allows the students to use the target language and share their ideas in every step of writing (pre-writing, drafting, revising and editing). By following these steps, the students gradually have knowledge of how to write a good paragraph by considering aspects of writing (content, organization, vocabulary, language use, and mechanics).