An outcome of science education is that young people have the understandings and skills to participate in public debate and make informed decisions about science issues that influence their lives. Toulmin's argumentation skills are emerging as an effective strategy to enhance the quality of evidence based decision making in science classrooms. In this case study, an Australian science teacher participated in a one-on-one professional learning session on argumentation before explicitly teaching argumentation skills to two year 10 classes studying genetics. Over two lessons, the teacher used whole class discussion and writing frames of two socioscientific issues to teach students about argumentation. An analysis of classroom observation field notes, audiotaped lesson transcripts, writing frames and student interviews indicate that four factors promoted student argumentation. The factors are: the role of the teacher in facilitating whole class discussion; the use of writing frames; the context of the socioscientific issue; and the role of the students. It is recommended that professional learning to promote student argumentation may need to be tailored to individual teachers and that extensive classroom based research is required to determine the impact of classroom factors on students' argumentation.