The study was designed as a linked two-phase investigation, aiming to psychometrically develop and validate a Chinese version of the "Organizational Climate Diagnostic Instrument for Junior High Schools" (OCDI-JH) for use in Taiwan. Through extensive literature reviews, the complex phenomena of school climate were decomposed into a priori school climate construct in the first phase of the study. The data were collected from two separate samples of 287 junior high school principals/teachers/administrators for exploratory factor analysis (EFA) and 295 for confirmatory factor analysis (CFA), which were performed to scrutinize the psychometric properties of the OCDI-JH comprising 22 items clustered under five dimensions of (a) Safety (three items), (b) Academic (three items), (c) Relationships (seven items), (d) Institutional Environment (five items), and (e) Leadership (four items). Importance-Performance and Gap Analysis (IPGA) was applied in the second-phase elicitation study on 15 school faculty members to detect climate factors to be strengthened in a selected junior high school for school improvement. Focusing explicitly on contextually specific evaluation that facilitate school improvement, the OCDI-JH offers promise as a robust school climate diagnostic appraisal with practical implications for improving school effectiveness and implications for future research directions.