The present study examines the usage patterns of stance that constructions in Korean EFL learners' written corpora by two different proficiency groups (KEFL 1, KEFL 2) to figure out some developmental features of marking stance in L2 academic prose. Focusing on three main categories (stance verbs, adjectives, and nouns) controlling stance that clauses, the study compares the frequency of each feature by the categories and their subcategories across the corpora. Employing both quantitative and qualitative analyses, the study found a marked developmental path across the corpora as a cross-sectional study. Indeed, less proficient L2 learners tended to use spoken involvement features as ‘a subjective transmitter’, emphasizing the writer's view only with a private authorial voice. However, more advanced learners showed remarkable features as ‘an objective interpreter’ with more implicitly detached stances. Despite a few chunk expressions considered as being memorized, more complex grammatical resources appropriate for academic discourse were observed. Finally, as the final stage, this study suggests ‘a refined stance-taker’ referring to an expert writer in the academic discourse community, which may be devoid in untrained native speakers' writing. In accordance with the need for university students to transition into more advanced academic discourse sooner, this study provides some practical insights into teaching and learning of stance patterns in using that complement clauses in English academic discourse.