The purpose of this quasi-experimental study was to explore the impact of asynchronous discussion on the quality and complexity of college students' arguments. Three different cohorts of students registered in a physical science course in 2009 Fall, 2010 Spring, and 2010 Fall semesters were briefly supported with scaffolding in class and then involved in argumentation about socio-scientific issues as take-home assignments. Each cohort was divided into an asynchronous online communication group and a paper-pencil group. The findings showed that very few students' arguments from either group were rated low in quality levels of 1 or 2 on a five-scale level. Additional comparisons revealed that the asynchronous online communication group students slightly outperformed their counterparts in terms of mean quality level of arguments (effect sizes ranged from 0.25 to 0.35) and the frequency of rebuttals. The major finding is that after only one hour of scaffolding followed by the opportunity to practice argumentation at home, students' argumentation skills were slightly better developed through reflective asynchronous online discussions about socio-scientific issues than through paper-pencil practice. (Contains 3 tables and 2 figures.)