Although Montessori is the most common unconventional education model, no multi-state study has compared standardized test proficiency of Montessori schools with districts. Here we report on this for the 10 states/regions with the most public Montessori schools (n = 195). In 3rd grade, Montessori schools were less proficient in math but more proficient in ELA. In 8th grade they were also more proficient on ELA and showed a trend to greater proficiency in math. Black, Hispanic, and economically disadvantaged students at Montessori schools were more proficient on ELA tests, and performed better or similarly on math tests, at both grade levels. Achievement gaps were generally smaller. Difference in percent proficient in 8th grade controlling for 3rd grade was consistently greater at Montessori schools than in districts. Potential reasons for the different performance of Montessori schools are discussed.