Grid-based measures, where item stems are rated across diverse domains or subjects, represent an economic measure to assess multifaceted constructs such as academic self-concept. Although testing for measurement invariance between groups (e.g., based on gender or age) and within subjects over time (e.g., in longitudinal research) is common practice, research on invariance across domains is still lacking. We examine measurement invariance across selected self-concept domains in the Differentiated School Self-Concept (DISC) Grid as an example of grid-based self-concept measures. Using a highly diverse student sample, we assessed invariance of the DISC grid across three academic domains (German, English, and mathematics). Based on adequate model fit within each domain, the DISC grid proved to be strictly invariant across the three subject-specific self-concepts (German, English, and mathematics). Implications for theory (e.g., Möller and Marsh’s Dimensional Comparison Theory), empirical research (e.g., on the Internal/External Frame of Reference model), assessment (e.g., regarding other measures using similarly worded items across domains, such as the Self-Description Questionnaires [SDQ]), and practice (e.g., academic counseling) are discussed.