Previous research on Montessori preschool education is inconsistent and prone to analytic flexibility. In this preregistered study, disadvantaged preschoolers in a French public school were randomly assigned to either conventional or Montessori classrooms, with the latter being adapted to French public education. Adaptations included fewer materials, shorter work periods, and relatively limited Montessori teacher training. Cross-sectional analyses in kindergarten (N = 176; M age = 5-6) and longitudinal analyses over the 3 years of preschool (N = 70; M age = 3-6) showed that the adapted Montessori curriculum was associated with outcomes comparable to the conventional curriculum on math, executive functions, and social skills. However, disadvantaged kindergarteners from Montessori classrooms outperformed their peers on reading (d = 0.68). This performance was comparable to that of advantaged children from an accredited Montessori preschool.Social and economic disparities have a tremendous impact on the academic, cognitive, and socioemotional development of children and adolescents. For example, in the United States and across Europe, socioeconomic status (SES) explains up to 15% of the variance in reading and math performance of highschoolers (OECD, 2016). Disadvantaged children also lag behind more advantaged peers on measures of cognitive and socioemotional abilities (Farah, 2017). These SES-related differences emerge as early as age 4 and tend to grow over time (Jordan & Levine, 2009; OECD, 2016). Thus, it is increasingly believed that interventions aimed at reducing inequalities should focus on early childhood, a period of enhanced brain plasticity during which cognitive skills may be the most responsive to cognitive and social stimulation (Thomas & Knowland, 2009). This has led to a renewed interest in preschool programs as a way to reduce the influence of SES disparities on early childhood development (Campbell et al., 2014;Duncan & Magnuson, 2013).Interest in early childhood education emerges from a large body of evidence showing that structured preschool programs can have a positive impact on school readiness and cognitive development of disadvantaged children (Campbell et al., 2014;Heckman, Moon, Pinto, Savelyev, & Yavitz, 2010). To date, policies have largely focused on structural factors such as teacher qualification (Jackson, Rockoff,We owe a debt of gratitude to A. Gascher and all of the teachers from both schools. This research would not have been possible without their involvement and dedication to the project. We also thank A
