This qualitative study had the objective of analyzing the influence of graphic organizers on the development of written argumentative tasks in a group of sixth-grade Colombian L2 English learners. Learners are increasingly required to analyze information presented in languages other than their first critically to form reasoned opinions and solve problems. It is thus urgent to develop their argumentation skills, needed not only for academic success but also later professional life--and, indeed, by participant citizens in democratic societies. Although there has been some increased interest in teaching argumentation at primary and secondary levels, this remains relatively unexplored Colombia, certainly when considering writing in a second language. For the present study, data were collected through a questionnaire, a survey, a focus group, a teachers' journal, and students' written artifacts and analyzed through the grounded theory approach. Findings revealed that using graphic organizers influenced learners' argumentative writing skills positively, specifically through supporting strategic information planning and argumentative linearization during the pre- and while-writing stages. These understandings, which show that younger learners can develop complex argumentative writing skills in a second language, offer significant lessons for teachers of language--and content--in both the first and additional languages.