The article raises questions about how argumentation is situated in science and religious education. Argumentation is about the justification of claims with reasons and evidence. It is a way of reasoning in both science and religious studies. A current 3-year research and development project entitled "Oxford Argumentation in Religion and Science" (OARS), lasting from 2018-2021 and based in England, aims to develop, implement and evaluate a teacher's professional development programme in order to nurture teachers' pedagogical skills in teaching argumentation in both science and religious education. The particular interest is in understanding complex judgments, especially where they integrate judgments from the sciences and religion. Hence, a key component of the project is to compare arguments from the sciences with arguments made in religion drawing out implications for teaching and learning. The setting of the project is in secondary schools in and focuses on Key Stage 3 (or 11-14 years-old pupils). Thirty teachers from 15 schools, including a range of faith/maintained, religiously plural/religiously uniform[LlV1], as well as secular state schools are participating in the project. Overall the project highlights the need for teachers' professional development to deal with complex argumentation that concern both science and religious education content.