This study explores the validity of the Culturally Responsive Instruction Observation Protocol (CRIOP) an instrument that measures the implementation of culturally responsive instruction (CRI) in K-8 classrooms with multilingual students. The validity study uses a Rasch measurement approach. With strong findings from analyses, including dimensionality and acceptable fit statistics, the instrument exhibits excellent internal structure, with stability and reliability across included categories. Furthermore, the instrument incorporates concepts specific to multilingual students across each pillar of culturally responsive instruction. The CRIOP offers a valuable means of evaluating CRI use in linguistically and culturally diverse K-8 classrooms, serving as a guide for teachers implementing CRI and for informing professional development efforts.