This study explored the effectiveness and second language (L2) writers' perceptions of process-oriented writing, using portfolio-basedinstruction in a secondary English class at general school settings. The participants were 110 high school students enrolled in a private independent school in Gyeonggi. They learned to produce a four-paragraph-English-essay based on the process-oriented writing methodology, keeping a portfolio note for the entire semester. The instructor was a bilingual teacher of English whose native language is Korean. The 17 weeks' records written in the portfolio note were analyzed to portray whether the approaches enhanced overall performance and understandings about essay-writing. Findings revealed that the participants were satisfied with this approach and improved their writing skills using portfolio-based- instruction. For the sake of implementing the new assessment appropriately at public school settings, further studies are suggested to develop how to enhance classroom environment in order to increase the degree of learner-satisfaction in the essay-writing classes.