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.

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.

Read the full research article about Montessori education by Jill Barshay at The Hechinger Report.