Extensive but separate bodies of research in education concern the constructs of school climate and school connectedness/belonging. In the interests of advancing a more integrated approach, a new measurement tool is developed– the School Climate and School Identification Measure–Student (SCASIM-St). This scale builds on the Moos (1973) framework which assesses relationships, personal growth, and system management in schools. The social identity approach to group processes (Tajfel & Turner, 1979; Turner, Hogg, Oakes, Reicher, & Wetherell, 1987) is used to extend work on school connectedness and belonging through the inclusion of a measure of social identification. A range of methods across three studies are designed to assess the reliability and validity of SCASIM-St (N = 7209, Australian grades 7–10 students). These include confirmatory factor analysis, test-retest analysis, and convergent validity (Study 1 and 2). Additionally measurement invariance tests for student sub-groups regarding gender, grade level, and non-English language, were employed in Study 3. It also included criterion validity analysis using multilevel models for the key outcome measures of students’ academic achievement, well-being, and aggressive behaviors. All of these analyses indicate that SCASIM-St is an effective measure. Theoretical and practical implications as well as future directions are outlined.