Geography education can facilitate learners' critical thinking and argumentation skills to make well-reasoned decisions on social and environmental issues. This study reports on a geography course consisting of 18 lessons, each of them 75 min, designed to afford intensive practice in argumentation to upper secondary school students (n = 21) and following the dramatic arc. The study produces examples of different developmental pathways of upper secondary school students' argumentation during the geography course. In this qualitative case study, the data were collected from learning diaries and analyzed using content analysis following ARRA-analysis (Analysis of Reasoning, Rhetorics and Argumentation), which is based on Toulmin's argumentation model. The results indicated that most of the students developed justified arguments and composed clear claims and relevant rhetorical modes such as qualifications, rhetorical questions and rebuttals. Justification categories that were mainly used were backings, grounds and warrants. However, some students had difficulties in recognizing the main claim and arguments. The students developed their argumentation skills following the dramatic arc. They possessed the prerequisites for argumentative reasoning and writing but needed further practice in analytical and critical writing.