Argumentation is a complex intellectual skill essential for academic achievement in a range of scholarly disciplines. Argumentative writing demands effective coordination of language use, reasoning processes, and background knowledge about a given topic. It is a cognitively challenging activity, especially for students learning English as a Foreign Language (EFL). The Dialectical Map (DMap) is an open-source argument visualization tool that scaffolds argument analysis, evaluation, and construction. A quasi-experiment was conducted with 190 undergraduate EFL students to investigate the pedagogical value of DMapping as a pre-writing activity. The research also explored the effect of DMapping on student motivation in learning argumentation. We found the DMap functioned as an effective pre-writing tool for argumentative writing and promoted transfer of argumentation skills. DMapping facilitated more balanced arguments, and students reported positive experiences and attitudes toward learning argumentation with the DMap. This paper concludes with implications and future research directions for using the DMap as a cognitive tool to foster meaningful learning.