Green School intend to increase student connection to the environment, and have the potential to increase achievement through opportunities for hands-on science learning. This study utilizes publicly available data on all public schools in Maryland to examine the extent to which the Green School designation relates to changes in science proficiency. Specifically, methods use mixed regression models of school-level science proficiency rates on the number of years as a Green School and predictive school characteristics to determine the association between time as a Green School and student science outcomes over two decades. This study improves upon existing research with timely data and methods to account for factors that may have biased previous findings.