This thesis is an expedition into and beyond students’ mathematics talk in classrooms framed by migration as a matter of dichotomization betweennamed languages and (in)formal aspects of one fixed mathematics. It is an attempt to make sense of how students grapple with and move about thedivides that those dichotomizations shapes. I ask; How do students in a Grade 5 classroom framed by migration navigate language andepistemological divides when talking about mathematics? and What theoretical conceptualization of epistemological dimensions of languagediversity can be used to frame the students’ navigation of the divides?‘Navigation’ and ‘navigate’ are the metaphors I use for finding one’s way in spaces that do not have established paths to follow. In this thesisepistemological divides articulate difference when individuals and/or cultures take and treat something as mathematical knowledge. They emergewhen people do and talk about mathematics. My focus is not primarily on how students learn mathematics through their navigation, but rather onhow the students inhabit the learn-ing space together—how they relate to each other—as they navigate.To grapple with the research questionsabove, to learn about multiple relational aspects of how students navigate language and epistemological divides when they talk about schoolmathematics, I have used a flexible research design in a multilingual, yet ‘Swedish-only’ Grade 5 (students aged 11) classroom in the south ofSweden. Theoretically I bring together a) linguistic inferentialism as an alternative to the representation paradigm, b) social interaction andecological approaches on knowledge to frame the relationship between language and c) mathematics in students’ talk in a classroom with a complexdiversity of languages and socio-economic backgrounds.Results show that when students in the Grade 5 class navigated language and epistemological divides they demonstrated solidarity andsometimes perform aggressive actions towards each other in their encounters with mathematical knowledge and language diversity. Theseperformances were theoretically conceptualized as meta-understanding of multilingualism (MULD) or lack of MULD. The performances areunderstood as connected to the mathematics based discursive spaces (MBDS) that emerged when the students discoursed.The present thesis contributes to the field by taking an ecology-based relational approach towards language and epistemology in order to providetools for considering students’ responsive translanguaging in multilingual classrooms with no shared languages (except the language of instruction).In addition, this thesis is the first to use inferentialism for ecology-based approaches on social epistemological issues of multilingualism inmathematics education research.