This paper discusses the design of an instructional unit examining scientific argumentation with prospective biology teachers. Linguistics and philosophy of science have turned to argumentation as a relevant skill; its importance in science classes has also been highlighted by scholars. We define school scientific argumentation and analyse its components. We present the unit, directed to pre-service biology teachers, which includes different strategies; among them, we propose guided reading, analogies, debates, and discussion on historical episodes. We describe the activities, examining the nature-of-science topics addressed. The sequence relates to secondary science teaching; this may increase the meaningfulness of the nature of science in teacher education.