Policy evaluation is essential to determine the success of the policy implementation in achieving its objectives. For evaluation purposes, a set of valid and reliable instruments is needed in order for the data could describe the object being measured. It is necessary to use a child-friendly school assessment instruments (CFS-AI) when the child-friendly policy is implemented. This research aimed to develop a measurement instrument of child-friendly school policy and program in elementary school with the Context, Input, Process, and Product (CIPP) evaluation model. The research used a quantitative-qualitative approach as suggested by Onwuegbuzie (2010), which an assessment instrument developed with mixed-methods analysis. The sample of this research consist of teachers, principals, parents, and community members around the school. The data were analyzed by Exploratory Factor Analysis (EFA) using the SPSS program to determine the validity and reliability of an instrument. The results showed the child-friendly school assessment instrument (CFS-AI) developed in four assessment aspects has fulfilled the requirements of validity and reliability. It implies that CFS-AI has fullfilled the standards to measure the success of the implementation of child-friendly schools in elementary schools. This instrument is comprehensive, precise, and consistent to measure the implementation of child-friendly school policy.