The aim of this research was to explore Australian high-school students’ argumentation andinformal reasoning about biotechnology. Data were obtained from semi-structured interviews with10 Year-8 students (12–13 years old), 14 Year-10 students (14–15 years old) and 6 Year-12students (16–17 years old) from six metropolitan high schools in Perth, Western Australia. Thetranscripts were analysed using both Toulmin’s argumentation pattern and informal reasoningpatterns (rational, emotive, and intuitive) as frameworks. The notion of scientific literacy was usedas the basis of the theoretical framework to examine the data. Most students used no data or onlysimple data to justify their claims. Students of all year groups used intuitive and emotive informalreasoning more frequently than rational. Rational informal reasoning was associated with moresophisticated arguments.