The purpose of this study was to examine changes in the quality of science teachers' argumentation as a result of their engagement in a teacher workshop on earthquake engineering emphasizing distributed learning approaches, which included concept mapping, collaborative game playing, and group lesson planning. The participants were ten high school science teachers from US high schools who elected to attend the workshop. To begin and end the teacher workshop, teachers in small groups engaged in concept mapping exercises with other teachers. Researchers audio-recorded individual teachers' argumentative statements about the inclusion of earthquake engineering concepts in their concept maps, which were then analyzed to reveal the quality of teachers' argumentation. Toulmin's argumentation model formed the framework for designing a classification schema to analyze the quality of participants' argumentative statements. While the analysis of differences in pre- and post-workshop concept mapping exercises revealed that the number of argumentative statements did not change significantly, the quality of participants' argumentation did increase significantly. As these differences occurred concurrently with distributed learning approaches used throughout the workshop, these results provide evidence to support distributed learning approaches in professional development workshop activities to increase the quality of science teachers' argumentation. Additionally, these results support the use of concept mapping as a cognitive scaffold to organize participants' knowledge, facilitate the presentation of argumentation, and as a research tool for providing evidence of teachers' argumentation skills.