This paper introduces the Critical Principles of Assessment Model, a conceptual framework designed to improve assessment literacy among pre-service music teachers (PSMTs) in Australian initial music teacher education (IMTE) programs. Grounded in social justice and aligned with the United Nations’ 2030 Agenda for Sustainable Development (UN, 2015), the model integrates Brophy and Fautley’s (2017) international principles for assessment in music education with Brookfield’s (2017) four lenses of critical reflection. It responds to persistent inequities in classroom music assessment that reproduce exclusionary practices, often shaped by identity, bias, and entrenched assessment habitus (Bourdieu & Richardson, 1986; Costa & Murphy, 2015; Plastow, 2023). Despite more than two decades of scholarship documenting idiosyncrasies in music assessment practices (Fautley & Murphy, 2014; Leong, 2014; Murphy, 2007; Russell & Austin, 2010; Wong, 2013; Zandén & Ferm Thorgersen, 2014), recent studies indicate little progress in disrupting exclusionary assessment traditions (Plastow, 2023). Pre-service teachers often replicate assessment practices drawn from their own musician identities and formative experiences (Fredrickson, 2007; Randles, 2013), privileging Western art music traditions and disadvantaging students from Indigenous, culturally and linguistically diverse, and low socio-economic backgrounds (Education and Training Committee, 2013; Elpus, 2022; Gurgel, 2015; Nieminen, 2022). These inequities directly contradict SDG Goal 4 (Quality Education) and Goal 10 (Reduced Inequalities).The Critical Principles of Assessment Model positions critical reflection as central to assessment literacy development. Brookfield’s four lenses—autobiography, students’ eyes, colleagues’ experiences, and theoretical literature—are aligned with assessment principles of authenticity, alignment, quality, operability, purpose, valuing, and social justice (Brophy & Fautley, 2017). By interrogating bias, identity, and long-held assumptions, the model creates productive “dilemmatic spaces” (Plastow, 2023) in which PSMTs confront conflicts between personal beliefs and professional knowledge. A pilot study with 77 pre-service music teachers demonstrated the model’s capacity to shift perceptions and practices. Initially, most participants judged a state-sanctioned composition task as fair and valid. However, after engaging with the model, they identified its lack of authenticity, validity, and inclusivity, exposing biases embedded in task design and valuing. PSMTs subsequently produced assessment tasks of significantly higher quality, judged by external reviewers to exceed typical standards. This paper argues for structural change in IMTE to embed critical reflection and principled assessment frameworks as central components of teacher preparation. The Critical Principles of Assessment Model offers a future-oriented approach to cultivating assessment literacy that disrupts entrenched inequities and fosters inclusive, socially just classroom music practices.