“…In doing so, we focus on the domain of geometry because it is a key area in which proofs and proving are learned and used in secondary school mathematics. While there have been numerous studies on proof and proving in secondary school geometry covering students' capabilities regarding proofs and their perspectives on proving in classes (Herbst & Brach, 2006;Hoyles & Healy, 2007;Senk, 1985), teachers' conceptions of proof (Knuth, 2002a(Knuth, , 2002b, textbook analysis (Fujita & Jones, 2014;Otten, Gilbertson, Males, & Clark, 2014), task design (Cirillo & Herbst, 2012;Komatsu, in press), and classroom-based research, including investigation of student-teacher interactions and teaching interventions to enhance student learning (Martin, McCrone, Bower, & Dindyal, 2005;Miyazaki, Fujita, & Jones, 2015), only a few studies have related to proof validation, mostly focusing on whether students can discern the invalidity of circular arguments (in which conclusions are used as suppositions). For instance, McCrone and Martin (2004) surveyed 18 American high school students and showed that only 22% of the students correctly judged a circular argument invalid.…”