In this chapter, we report on a small-scale critical mathematics education project in a Swedish classroom with students of varied language backgrounds. The project departed from the student Arvid's statement "Mathematics is bad for society." Our research interest was twofold. On the one hand, we wanted to explore what knowledge is being (re)produced by students as they try to connect and reason with a statement like "Mathematics is bad for society." And on the other hand, we were also interested in how the students in this classroom, in which they do not have shared mother tongues, can express and (dis)acknowledge knowledge when reasoning about mathematics in society. We found that when the students (and their teacher) grappled with unpacking critical aspects such as "mathematics in society," their reciprocal assessment of claims was based on their individual ways of knowing and talking, and tended to shape both their actions and the outcome of their efforts. We show that the discussion around critical aspects of mathematics in society that came to the fore was intertwined with both students' and the teacher's (lack of) meta-understanding of language diversity.