Explore how the Mathematics Proficiency Test (MPT) in Ontario, Canada delivers scalable, inclusive teacher candidate test for certification through thoughtful system design. Introduced in response to declining student mathematics performance, the MPT was developed to ensure all teacher candidates demonstrate essential mathematical knowledge and pedagogical skills before entering the profession. Administered to over 10,000 candidates annually, the test offers both remote and in-person formats across a province larger than Texas, with bilingual delivery, extended test windows, and results delivered within days. The platform is fully accessible, meeting WCAG 2.0 AA standards and following Universal Design principles. Supported by a unified portal, real-time coordination between operational partners, and structured feedback from candidates and stakeholders, the MPT strikes a balance between accessibility, integrity, and rigour for inclusive, high-stakes certification.