The purpose of this study was to explore the impact of argumentation-based pedagogy on college students' conceptual understanding of properties and behaviors of gases. The sample consists of 108 students (52 in the control group and 56 in the intervention group) drawn from 2 general chemistry college courses taught by the same instructor. Data were collected through pre- and post-tests. The results of the study show that the intervention group students performed significantly better than the control group students on the post-test. The intervention group students also showed significant increase in their test scores between pre- and post-test. While at least 80% of the students in the intervention group abandoned their initial ideas on all of the 17 alternative conceptions that were identified by the authors but one, the percent of student abandoning their initial ideas in the control group was less than 50. The discussion focuses on the implications of these results for addressing students' alternative conceptions, promoting the argumentation-pedagogy in college science courses and the challenges associated with the use of argumentation in college science classrooms.