This paper explores how five third-graders constructed meaning in three school-based literacy participation structures, also examining teachers' invitations and the space they make for students' talk and students' comprehension practices. High-stakes assessments and mandated reading curriculum influence how comprehension is framed and how students are invited to engage in discussions about text. Students' opportunities to exercise textual agency are often limited. However, when students had greater control over the discussion and the authority to evaluate the written text and their peers' comments for accuracy or plausibility, their comprehension was strengthened. Students actively constructed meaning as they considered multiple, possible interpretations, while also taking into account their own personal experiences and other valuable social and semiotic resources. (Contains 2 tables and 1 figure.)