This article examines how a teacher utilized a sandwich approach to DA in a sixth grade Spanish World Language classroom to form a dialectical relationship between instruction and assessment. While existing research has provided evidence that mediation provided during group DA can promote the language learning of multiple students, these investigations presented data for only a few individuals in the group, rather than all. The present study explored how DA was used in the classroom to gather more accurate data on all learners so that instruction could be tailored more appropriately to individual’s needs. In the present study, the teacher delivered a pretest, analyzed students’ performance to design instructional modules, and then carried out a series of posttests and transfer tasks to determine learners’ mediated performance. Our findings focus on how the teacher’s analysis of student performance shaped her subsequent instructional decisions and interventions.