Background: The whole school, whole community, whole child (WSCC) model provides a framework for schools to support student health and academic achievement, however, implementation is a complex organizational change requiring the collective efforts of the school organization to be successful. Over half of all failed complex organizational change efforts, such as WSCC implementation, can be attributed to a lack of readiness. The ability to accurately assess school organizational readiness to implement the WSCC can improve preparation and processes necessary to promote successful and sustainable change. Purpose: The purpose of this study was to develop and validate a theory of organizational readiness for change (TORC)-based instrument to assess school organizational readiness to implement actions that support the WSCC model. Methods: A non-experimental, cross-sectional study design was employed with 271 public school employees from 43 schools. An instrument was drafted which operationalized readiness to implement the WSCC as eight actions supported in the literature to facilitate effective implementation. Instrumentation consisted of face and content validity by a panel of experts, stability reliability by test-retest, internal reliability applying Cronbach’s alpha, interrater agreement and reliability applying intraclass correlations and rwg(J) index, construct validity applying confirmatory factor analysis, and predictive validity applying multiple linear regression analysis. Results: Measures of interrater reliability and agreement supported the aggregation of individual-level readiness perceptions to the organization level of analysis for both general change commitment (GCC) (rwg(J).uniform=0.95, rwg(J).skew=0.79, ICC1=0.43, ICC2=0.91, p<.01) and general change efficacy (GCE) (rwg(J).uniform=0.95, rwg(J).skew=0.80, ICC1=0.49, ICC2=0.93, p<.01). The final structural model exhibited reasonable fit of the data (χ2=751.93, df=295, p<.001; GFI=0.833; AGFI=0.801; NFI=0.901; CFI=0.930; RMSEA=0.076). Both GCC (β=.589, p<.001) and GCE (β=.354, p<.001) were significant predictors of change-related effort, accounting for 77% of the variance. Overall, reported change-related effort was low (M=6.07; SD=2.70) with 74% of the scores below the scale midpoint. Discussion: A valid and reliable TORC-based instrument was developed to assess school organizational readiness to advance implementation of the WSCC model. Future research may seek to examine potential moderators and mediators of the TORC constructs in order to fully operationalize the theoretical framework.