Constructing and critiquing scientific arguments has become an increasingly important goal for science education. Yet, the differences in the ways students construct collaborative oral and individual written socioscientific arguments are not well established. Our research with one middle school class in an urban New England school district addresses the following question: What are the similarities and differences between students' collaborative oral and individual written scientific arguments? Data sources consisted of transcripts from three videotaped lessons and associated student work. The sophistication of both the collaborative oral and individual written argument products were analyzed using a proposed learning progression. Results suggest that the students' collaborative oral arguments tended to be of lower sophistication whereas the individual written arguments tended to be of higher sophistication; however both modalities tended to include inappropriate justifications. Moreover, in the written arguments it was easier for students to include a rebuttal than limit their argument to using only appropriate justifications. These findings suggest that there are both commonalities and differences across the expressive modalities that can be targeted in an effort to strengthen the quality of students' arguments.