AbstractThis descriptive research work highlights the implementation practices of Montessori education in mainland China and the concerns over Montessori education’s localization in mainland China. Localization can be understood as the adaptive process Montessori education undergoes in order to fit within Chinese culture. Two hundred and ten in-service Montessori teachers and administrators in China were surveyed to discover information concerning implementation practices in the following areas: mixed-aged classrooms, whether classrooms were co-teaching, student-to-teacher ratios, and morning and afternoon work cycles. The study found that the majority of classrooms were mixed-aged, reflecting high-fidelity Montessori practices. However, it also found that classrooms are co-teaching, have lower student–teacher ratios, and shortened work cycles, reflecting a departure from high-fidelity Montessori implementation. While localization should be considered to safeguard Montessori education’s sustainability, Chinese Montessori educators should also reflect on these findings as high implementation fidelity has been linked to better student outcomes.