By The Hechinger Report, Contributor

MONTESSORI SCHOOLS HAVE many loyal devotees and they’re certainly rising in popularity among American parents. But are they any better than traditional schools, or other progressive teaching philosophies?

You’d think we’d know the answer to that question by now. Montessori schools have been around for more than a hundred years, dating back to Maria Montessori’s first school for poor children in Rome in 1907. In recent years, there’s been a surge in new Montessori schools in the United States, fueled, in part, by new state laws that are expanding the numbers of publicly funded, but privately run charter schools.

Today there are some 500 publicly funded Montessori schools across the United States, up from fewer than 300 in 2000, according to the National Center for Montessori in the Public Sector. The number of private Montessori schools, estimated to be around 4,000, is rising too. (Full disclosure: my daughter attends a Montessori school and I went to a Montessori kindergarten.)

Yet there’s been very little rigorous research to prove that children learn more in Montessori schools than they otherwise would have. The main problem is that you can’t randomly assign some students to Montessori schools and study how they do compared with students at traditional schools. Parents get to make these choices, and it’s quite possible that the parents who choose Montessori schools are more academically inclined than those who don’t.

Thanks to the expansion of publicly funded Montessori schools, with lotteries and waitlists to get in, researchers are now able to study the matter more rigorously. That’s because lotteries are, in effect, a random assignment machine. Some kids win a seat in a Montessori school. Others don’t. And you can compare the achievement of the lottery losers with the lottery winners.

Recently, two peer-reviewed studies were published using this methodology. The results are mixed: promising for preschool, not so promising for older students in high school.

In the October 2017 preschool study, published in Frontiers in Psychology, six researchers looked at two Montessori schools in Hartford, Connecticut. Both were established by the state as public “magnet” schools, designed to be very high-quality Montessori programs that would attract wealthy families from the suburbs to low-income neighborhoods in Hartford. Some of the students who attended the public Montessori schools had family incomes as high as $200,000 a year. The students who “lost” the lottery all ended up at some other sort of preschool. Half of them attended a private school; others went to a federally funded Head Start program.

The researchers tested approximately 140 students at the start of the preschool and found that both the Montessori and non-Montessori kids began at age three with similar achievement scores. The 70 students who went to the Montessori schools advanced more rapidly on math and literacy tests over the next three years. At the end of kindergarten, when this study ended, the Montessori kids had significantly higher achievement. (Softer skills, such as group problem-solving, executive function and creativity were not better for Montessori kids. The two groups did about the same on those measures, or the differences were not statistically significant.)

To be sure, high-income kids outperformed low-income kids regardless of the school. But the researchers found that lower-income kids in Montessori schools had much higher math and literacy scores than the lower-income kids in other schools. Similarly, higher-income kids in Montessori outperformed higher-income kids in other schools, but not by as much.

One question is whether it’s the Montessori method that’s driving the results, or whether these Hartford children benefited from especially good teachers who would have gotten these results regardless of the teaching method. One theory is that gifted educators are particularly drawn to Montessori philosophy and study for the extra certifications.