Following constructivist paradigms for learning, this article explores the relationships between the components of argumentation competence (knowledge, behavior and attitude), their relationships with domain-specific knowledge acquisition, and the differences in argumentation behavior between successful and less-successful students. An exploratory study, with a pre- and post-test design, in an authentic, non-scaffolded, online learning environment was conducted. Contrary to our expectations, no significant relationships between the components of argumentation competence were found. Nevertheless, a significant relationship between argumentation behavior and domain-specific knowledge acquisition was found. Moreover, results suggested that the capacity of students to transfer argumentation behavior to similar argumentation tasks can be related to students’ domain-specific knowledge acquisition. Finally, successful students in terms of domain-specific knowledge acquisition scored higher with regard to their argumentation behavior than less-successful students. These findings are discussed followed by theoretical and practical implications and suggestion for future work.