Internationally, there are calls for students to be able to use their scientific understandings to make informed decisions about the world in which they live. Using a mixed methods case study design, this study investigated the impact of behaviours and strategies used by two early career science teachers who taught argumentation about a water-based socioscientific issues (SSI) to their Year 7 students. Students' argument quality, measured using Toulmin's argument structure, improved significantly from pre- to post-instruction (p = 0.0033). There was also a significant increase (p = 0.0037) in the number of types of categories. Qualitative data comprising classroom audio-transcripts, field notes, student work samples, teacher interviews and student reflections were analysed using inductive analysis to identify four themes related to teacher behaviours and teaching strategies: (1) developing and maintaining a safe classroom environment; (2) providing clear instructions about the features of quality arguments; (3) providing opportunities for all students to think and work individually and collaboratively; and (4) practising oral and written argument construction with gradual removal of scaffolds. While the findings are not generalisable teacher educators can use their expertise to decide the extent to which the teacher strategies and behaviours would support the development of argumentation skills in their particular context.