Argumentation has long been promoted as a core scientific practice in which students should engage, yet science classrooms still often omit it. One remedy is to incorporate socioscientific issues (SSIs) in the curricula. SSIs are open-ended and complex, typically subject to multiple perspectives and solutions. These issues, influenced by science and society, are relevant to students' lives and promote classroom argumentation. Engaging in argumentation on SSIs requires students to discuss science content with their peers and teachers without setting out to defeat an opponent. Collaboration becomes important as students establish criteria to distinguish among multiple distinct ideas and work together to build a sound argument. The authors recommend using critical friend pairs, in which two students discuss and critique each other's arguments, to promote collaboration and critical-thinking skills. This article presents a lesson plan using critical friend pairs that promotes argumentation and evaluating evidence. Using the four-part activity design described in this article, students have multiple opportunities to revise a scientific argument based on evidential reasoning. Additionally, rather than declare a "winning" position, the critical friend pairs allow students to reach a consensus position, which is more realistic and useful. With this goal in mind, students will learn to evaluate claims for accuracy and read for evidence, rather than just comprehension. By pairing students into critical friend pairs, they can begin to differentiate between disagreeing based on emotion without evidence and being critical of a position. This practical ability can help in a variety of situations.