Studies of high school literacy intervention classes have measured reading gains through standardized assessments, but few have considered the impact on students' identities. In this embedded case study, I used theories of identity and positioning to answer two research questions: How did institutional and interpersonal acts of positioning in two literacy intervention classrooms build on, change, or challenge students' personal histories and identities as readers? How did these acts shape students' understandings of themselves as readers over time? I collected and analyzed interviews, field notes, and artifacts. Analyses revealed that ongoing positioning in one classroom thickened one student's identity as a poor reader. Positioning in the second classroom reinforced the other student's identity as a good student but had little impact on her identity as a reader. These findings highlight the need to better understand how instructional contexts privilege particular ways of reading and understandings of what it means to be a reader.