Context The pervasiveness of deficit-based discourses about multilingual students has long been documented in the scholarly literature. Such discourses severely erode the learning and well-being of multilingual youth. One of the spaces in which deficit-based discourses about students may be transformed is professional development. Focus of the Study The study connects a key practice of high-quality professional development, the analysis of classroom evidence of student learning, to student-focused discourses about multilingual youth. The research questions the study addresses are: As they make sense of data together, (a) how do teachers discursively position multilingual youth? and (b) what factors reinforce and undermine assets-based discourses about multilingual youth? Research Design Leveraging a case study approach, I explore how a team of three middle-school teachers positions students while analyzing classroom evidence during a one-year professional development designed for educators of multilingual youth. I rely primarily on transcripts of professional development sessions to trace student positioning by the team over time as teachers analyze dissimilar types of classroom evidence. Findings The findings reveal complex mediational relationships among teachers’ data use, student positioning, and shared theories of student engagement. These co-constructed theories reinforce deficit views of students when student reasoning and participation in learning are obscured by the data teachers are exploring. When the data make the process of student engagement available for reflection, however, teachers shift toward assets-based discourses. In addition, the findings shed light on relationships between type of evidence and implications for classroom practice. The teachers in the study shift their focus from teacher-centered instruction to the scaffolding of student interaction when the data make visible student participation in learning. Conclusions The study contributes to a nascent knowledge base about the complex relationships between teacher analysis of classroom evidence and assets-based discourses about all students and multilingual students in particular. The findings expand current conceptualizations of teacher data use by foregrounding student positioning over time as a key element of teacher sensemaking, and revealing the significant mediational role that shared theories of student engagement play in teachers’ data use. In terms of practical implications, the study offers insights into the mechanisms through which assets-based discourses about multilingual youth can be fostered across learning contexts.