This study presents an analysis of the consequences for students when performance assessment and differentiation practices are combined, as part of attempts to increase minimum standards within upper-secondary schooling. Recent standards-based curriculum reform in Australia demonstrates how a focus on minimum levels of achievement can limit the benefits of performance assessment and result in differentiation practices that define the learning contexts for specific groups of students and restrict their opportunities to learn and achieve. The conclusions presented are based on analyses of the revised curriculum design, as well as investigations into the implementation of the new curriculum within three schools. Teachers' planning documentation for learning and assessment, along with semi-structured interviews with school leaders, teachers and students, provided insight into school-based practices resulting from the revised curriculum. Analyses of both the curriculum and its early implementation reveal that standards-based reforms to curriculum can lead to differentiation practices that restrict outcomes for students who traditionally do not succeed in schooling. This study also demonstrates that the nature of the differentiation practices adopted by schools during the implementation of minimum standards depends on the prevailing perceptions and practices within local school contexts. (Contains 1 note and 1 table.)