Integrating basic principles, values, and practices of education for sustainability in early childhood education (ECE) is important for developing and developed countries. In this context, there is a need to identify and evaluate indicators that measure sustainable practices in ECE programs. This study was conducted in 18 preschools in Turkey to provide statistical analyses of the sustainability indicators. OMEP Environmental Rating Scale for Sustainable Development in Early Childhood with three subscales for sustainability (economic, environmental, and sociocultural) was utilized as the data collection tool. The reliability analyses are framed on generalizability theory, which identifies the sources of variation across schools, raters, and indicators on the three subscales. The study finds that the sustainability indicators can be redefined and adapted to be employed in the Turkish context as a way to ensure more reliable measurement of sustainability practices in early childhood education settings.