Practical educational assessment tools for adolescents champion student voice, use technology to enhance engagement, highlight discrepancies in school experience, and provide actionable feedback. We report a series of studies that detail an iterative process for developing a new school climate assessment tool: (1) item generation that centres student voice, (2) the design of a web-based app, (3) item revisions informed by student and educator feedback, and (4) the identification and confirmation of the underlying factor structure of the assessment tool. The resulting School Climate Walkthrough provides scores on nine dimensions of school climate and 73 additional observational items. The web-based application produces instantaneous reports that display systemic differences in how various student demographic groups experience school. This process can guide future research in building the next generation of educational assessments for adolescents and disrupting harmful or exclusionary school practices.