In this study, 15 prospective secondary (grades 6-12) mathematics teachers were asked to situate themselves as middle school (grades 6-8) mathematics teachers and validate arguments purported to prove that the sum of the first "n" odd natural numbers is "n"[superscript 2]. We examined their stated expectations for middle school students' mathematical arguments and the rationales given for these expectations. Even though the participants were situated as middle grades teachers when evaluating hypothetical student arguments, not all of the participants embraced this perspective when discussing their expectations for middle school students' arguments. In fact, only six participants embraced the teacher perspective, whereas nine participants relied, at least in some part, on their own experiences as students to determine their expectations for student work. In this article, we report five representative participants' expectations and rationales to illustrate three emerging perspectives on prospective teachers' expectations for middle school students' arguments.