School climate has a profound impact on the wellbeing of staff and students. Although existing measures are available to assess dimensions of school life (Bradshaw et al., 2021; Espelage et al., 2014), surveys that comprehensively assess components of school climate from multiple perspectives are needed. A rationale is presented for developing the New Jersey School Climate Improvement Survey for students, staff, and parents/caregivers, which varies from existing instruments in its measurement of unique domains; alignment of items across informant types; integration of diversity, equity, and inclusion items across domains; and ability to disaggregate by demographic characteristics, including student gender expansive categories. Internal consistency and structural validity were investigated using data from 5,504 students in grades 3-5, 16,280 students in grades 6-12, 5,464 staff, and 5,874 parents/caregivers. For each survey version, results support a correlated model structure and demonstrate strong internal reliability (e.g., omega coefficients above 0.70). Confirmatory factor analyses and Pearson correlations demonstrate strong internal structural validity across surveys. Implications are discussed, including how the instrument can inform a school climate improvement process that involves identifying strengths and needs, assessing the impact of interventions, and monitoring progress toward goals over time. Impact Statement This article advances an understanding of the reliability and validity of a new multi-informant school climate assessment known as the New Jersey School Climate Improvement (NJ SCI) Survey. The survey can be used by school support staff including school psychologists, to collect data used to inform school climate improvement to create supportive and equitable learning conditions in schools.