The debate over the most effective models for early childhood education is a longstanding one. While the benefits of preschool are widely accepted, researchers have observed that the academic advantages gained in many programs tend to diminish by the time children finish kindergarten, a phenomenon often called “fade-out.” Some studies have even pointed to potential negative long-term outcomes from certain public preschool programs, intensifying the search for approaches that provide lasting benefits.
This situation prompted researchers to rigorously examine the Montessori method, a well-established educational model that has been in practice for over a century. Their new large-scale study found that children offered a spot in a public Montessori preschool showed better outcomes in reading, memory, executive function, and social understanding by the end of kindergarten.
The research also revealed that this educational model costs public school districts substantially less over three years compared to traditional programs. The findings were published in the Proceedings of the National Academy of Sciences.
The Montessori method is an educational approach developed over a century ago by Maria Montessori. Its classrooms typically feature a mix of ages, such as three- to six-year-olds, learning together. The environment is structured around child-led discovery, where students choose their own activities from a curated set of specialized, hands-on materials. The teacher acts more as a guide for individual and small-group lessons rather than a lecturer to the entire class.
The Montessori model, which has been implemented in thousands of schools globally, had not previously been evaluated in a rigorous, national randomized controlled trial. This study was designed to provide high-quality evidence on its impact in a public school setting.
“There have been a few small randomized controlled trials of public Montessori outcomes, but they were limited to 1-2 schools, leaving open the question of whether the more positive results were due to something about those schools aside from the Montessori programming,” said study author Angeline Lillard, the Commonwealth Professor of Psychology at the University of Virginia.
“This national study gets around that by using 24 different schools, which each had 3-16 Montessori Primary (3-6) classrooms. In addition, the two prior randomized controlled trials that had trained Montessori teachers (making them more valid) compromised the randomized controlled trial in certain ways, including not using intention-to-treat designs that are preferred by some.”
To conduct the research, the research team took advantage of the admissions lotteries at 24 oversubscribed public Montessori schools across the United States. When a school has more applicants than available seats, a random lottery gives each applicant an equal chance of admission. This process creates a natural experiment, allowing for a direct comparison between the children who were offered a spot (the treatment group) and those who were not (the control group). Nearly 600 children and their families consented to participate.
The children were tracked from the start of preschool at age three through the end of their kindergarten year. Researchers administered a range of assessments at the beginning of the study and again each spring to measure academic skills, memory, and social-emotional development. The primary analysis was a conservative type called an “intention-to-treat” analysis, which measures the effect of simply being offered a spot in a Montessori program, regardless of whether the child actually attended or for how long.
The results showed no significant differences between the two groups after the first or second year of preschool. But by the end of kindergarten, a distinct pattern of advantages had emerged for the children who had been offered a Montessori spot. This group demonstrated significantly higher scores on a standardized test of early reading skills. They also performed better on a test of executive function, which involves skills like planning, self-control, and following rules.
The Montessori group also showed stronger short-term memory, as measured by their ability to recall a sequence of numbers. Their social understanding, or “theory of mind,” was also more advanced, suggesting a greater capacity to comprehend others’ thoughts, feelings, and beliefs. The estimated effects for these outcomes were considered medium to large for this type of educational research.
The study found no significant group differences in vocabulary or a math assessment, although the results for math trended in a positive direction for the Montessori group.
In a secondary analysis, the researchers estimated the effects only for the children who complied with their lottery assignment, meaning those who won and attended Montessori compared to those who lost and did not. As expected, the positive effects on reading, executive function, memory, and social understanding were even larger in this analysis.
“For example, a child who scored at the 50th percentile in reading in a traditional school would have been at the 62nd percentile had they won the lottery to attend Montessori; had they won and attended Montessori, they would have scored at the 71st percentile,” Lillard told PsyPost.
Alongside the child assessments, the researchers performed a detailed cost analysis. They followed a method known as the “ingredients approach,” which accounts for all the resources required to run a program. This included teacher salaries and training, classroom materials, and facility space for both Montessori and traditional public preschool classrooms. One-time costs, such as the specialized Montessori materials and extensive teacher training, were amortized over their expected 25-year lifespan.
The analysis produced a surprising finding. Over the three-year period from ages three to six, public Montessori programs were estimated to cost districts $13,127 less per child than traditional programs. The main source of this cost savings was the higher child-to-teacher ratio in Montessori classrooms for three- and four-year-olds. This is an intentional feature of the Montessori model, designed to encourage peer learning and independence. These savings more than offset the higher upfront costs for teacher training and materials.
“I thought Montessori would cost the same, once one amortized the cost of teacher training and materials,” Lillard said. “Instead, we calculated that (due to intentionally higher ratios at 3 and 4, which predicted higher classroom quality in Montessori) Montessori cost less.”
“Even when including a large, diverse array of schools, public Montessori had better outcomes. These finding were robust to many different approaches to the data. And, the cost analysis showed these outcomes were obtained at significantly lower cost than was spent on traditional PK3 through kindergarten programs in public schools.”
But as with all research, there are limitations. The research included only families who applied to a Montessori school lottery, so the findings might not be generalizable to the broader population. The consent rate to participate in the study was relatively low, at about 21 percent of families who were contacted. Families who won a lottery spot were also more likely to consent than those who lost, which could potentially introduce bias into the results.
“Montessori is not a trademarked term, so anyone can call anything Montessori,” Lillard noted. “We required that most teachers be trained by the two organizations with the most rigorous training — AMI or the Association Montessori Internationale, which Dr. Maria Montessori founded to carry on her work, and AMS or the American Montessori Society, which has less rigorous teacher-trainer preparation and is shorter, but is still commendable. Our results might not extend to all schools that call themselves Montessori. In addition, we had low buy-in as we recruited for this study in summer 2021 when COVID-19 was still deeply concerning. We do not know if the results apply to families that did not consent to participation.”
The findings are also limited to the end of kindergarten. Whether the observed advantages for the Montessori group persist, grow, or fade in later elementary grades is a question for future research. The study authors expressed a strong interest in following these children to assess the long-term impacts of their early educational experiences.
“My collaborators at the American Institutes for Research and the University of Pennsylvania and University of Virginia are deeply appreciative of the schools, teachers, and families who participated, and to our funders, the Institute for Educational Sciences, Arnold Ventures, and the Brady Education Foundation,” Lillard added.
The study, “A national randomized controlled trial of the impact of public Montessori preschool at the end of kindergarten,” was authored by Angeline S. Lillard, David Loeb, Juliette Berg, Maya Escueta, Karen Manship, Alison Hauser, and Emily D. Daggett.
