This paper extends the scholarship on attainment grouping by focusing on the policy initiatives of streaming and subject-based banding (SBB) in Singapore. The study is framed by the concept of pragmatic perfectionism, which refers to the continuous and ideals-oriented drive to improve a system through practical, incremental and paradoxical measures. It is argued that SBB is aligned with setting by giving students the flexibility and choice to study different subjects at varying levels. Mixed-attainment grouping is also evident, where students are grouped in mixed-form classes for selected subjects. However, SBB may have inadvertently maintained between-school segregation for elite and non-elite schools by supporting the existing policy of school posting based on students' exam scores. This paper contributes to the diverse formulations, adaptations and justifications surrounding attainment grouping. The study also illustrates the usefulness of pragmatic perfectionism in foregrounding the potential and tensions in educational policymaking.