If you’ve ever watched a small child spend what feels like forever pouring water between two glasses — not because anyone asked, but because they wanted to — you may have wondered whether it’s genius or whether you’ve failed at entertaining them. Turns out, it may be one of the most valuable things they do all day.
That’s the thing about Montessori. The “why” often only makes sense once you understand what’s happening inside a child’s developing brain — specifically, something called executive function.
BloomPath has been tracking the research on early childhood development for a while, and right now, there’s one study every parent choosing a preschool should know about.
TL;DR: A 2025 PNAS randomized controlled trial of 588 children across 24 public Montessori schools found that by kindergarten, Montessori kids scored significantly higher in reading, short-term memory, theory of mind, and executive function — with effect sizes of 0.22–0.30. Crucially, these gains grew over time instead of fading out, which is what most preschool research finds.
What Is Executive Function — and Why Should You Care More Than Grades?
Executive function is your brain’s air traffic control system. It manages three things:
- Inhibitory control — stopping yourself from blurting out the answer before you think. (Adults call this “impulse control.”)
- Working memory — holding information in your head while you use it. (“Where did I put that thought?”)
- Cognitive flexibility — switching between tasks and ideas without melting down.
Think of your toddler’s brain like a CPU with limited RAM and no built-in delay mechanism. Executive function is the firmware update that gradually installs between ages 3 and 7 — and it predicts long-term outcomes better than IQ scores in some studies.
Children with better self-control across ages 3–11 — a skill closely tied to executive function — grew into adults with better physical health, better personal finances, and less substance dependence and criminal offending at age 32. That’s not opinion — that’s from Moffitt et al. (2011) in PNAS, which followed about 1,000 children in Dunedin, New Zealand, from birth to age 32.
So: executive function matters enormously. Which brings us back to the preschool question.
What Did the 2025 PNAS Study Actually Find?
This was a randomized controlled trial — the gold standard of research design. Not a survey. Not “parents who chose Montessori rated it higher.” An actual lottery.
Researcher Angeline Lillard of the University of Virginia and her team followed 588 children (242 Montessori, 346 control) across 24 public Montessori schools in the United States. Children were entered at age 3 via competitive lottery — meaning the only difference between the two groups was luck of the draw, not family income or parental education.
Here’s what they measured at the end of kindergarten:
| Outcome Domain | Measure Used | Hedges’ g Effect Size |
|---|---|---|
| Executive Function (HTKS) | Head-Toes-Knees-Shoulders task | 0.222–0.297 |
| Working Memory | Forward/Backward Digit Span | ~0.20 |
| Reading | Letter-Word ID | Statistically significant |
| Social Understanding | Theory of Mind | Statistically significant |
| Overall Cognition | Combined domain average | 0.231 |
An effect size of 0.2–0.3 is modest but meaningful — comparable to the effect of high-quality tutoring on reading scores.
But here’s the finding that genuinely surprised me.
The “Fade-Out” Problem — and Why Montessori Breaks It
Almost every preschool study ever done shows the same disappointing pattern: kids gain skills in the program, and by second grade those gains have faded to near zero. It’s called the “fade-out” effect, and it’s why some researchers have questioned whether early childhood interventions are worth the investment.
The Montessori kids in this study did the opposite. At the end of PK3 and PK4, the differences weren’t statistically significant. But by the end of kindergarten — the third year of the 3–6 Montessori cycle, when roughly half of the Montessori group was still in a Montessori classroom — clear Montessori advantages had emerged.
Why? Lillard’s interpretation: Montessori trains durable cognitive skills, not rote content. When a child spends three years practicing self-directed focus, managing frustration without a teacher intervening every 90 seconds, and choosing their own work sequence — they build the mental architecture that actually transfers to new environments.
If you’ve ever seen a child finish one task and move on to the next without anyone telling them what to do, that’s executive function talking.
Is the Montessori Near You Actually Montessori?
Here’s the uncomfortable truth: the word “Montessori” is not trademarked or regulated. Any school can hang a sign and call itself Montessori.
The study specifically examined schools with meaningful fidelity to the method. When you’re evaluating a school, ask about these five things:
1. Multi-age classrooms (3–6 year olds together) This is non-negotiable. Younger children learn from older ones; older children consolidate skills by teaching. It’s built into the developmental model.
2. Uninterrupted 2–3 hour work blocks in the morning Montessori calls this the “work cycle.” This is when executive function practice actually happens — choosing work, sustaining attention, completing a task, putting it away. Schools that interrupt every 30 minutes with transitions are not delivering the model.
3. Trained teachers (AMI or AMS credentialed) Ask specifically: “Are your lead teachers AMI or AMS credentialed?” AMI (Association Montessori Internationale) and AMS (American Montessori Society) both require 1–2 year intensive training programs. A weekend certificate is not equivalent.
4. Materials, not worksheets Walk through the classroom. Are children working with physical materials — pink towers, bead chains, sandpaper letters? Or are they completing worksheets? The former is Montessori. The latter is not.
5. Observation policy Authentic Montessori schools invite parents to observe the classroom in action. If a school refuses observation visits, I’d walk away.
I’m not saying non-Montessori preschools are bad — there are excellent traditional programs. But if you’re specifically seeking the outcomes from this research, you need to verify fidelity to the method, not just the name.
What About Cost? (Real Numbers)
The PNAS study also found that three years of public Montessori costs $13,127 less per child than comparable traditional programs, largely because Montessori classrooms have higher child-to-teacher ratios in the younger years.
Private Montessori schools are a different story — they can run $15,000–$30,000/year in major US cities, which makes them inaccessible for most families. The exciting part of this study is that it focused specifically on public Montessori, which is free. Look up whether your district has a Montessori magnet or charter program.
Three Questions to Ask at Every School Tour
Most parents’ school-tour checklist is basically “is it clean?” and “do the kids look happy?” After this research, better questions are:
- “Can you walk me through a typical three-hour morning and how children choose their work?”
- “What specific training do your teachers have, and how long was it?”
- “What’s your policy on interrupting the work cycle for transitions?”
You’ll know a lot from how a director answers question one.
The Bottom Line
School information nights can be revealing: some directors spend 20 minutes on the parking lot and five on their educational philosophy. Ask about teacher credentials — and notice whether you get a real answer or a brochure.
The research is getting clearer. Executive function is a better predictor of a child’s future than almost any single metric we have. And a well-implemented Montessori program — delivered by trained teachers with fidelity to the method — appears to meaningfully develop those skills in a way that doesn’t fade.
You don’t need to choose Montessori. But you should understand what you’re choosing toward, not just away from.
Tracking your child’s developmental milestones? BloomPath has a free tool that maps milestones to executive function development stages — so you can see what’s happening in that little CPU of theirs.
You’re here reading this at 11pm. That already makes you a great parent.
FAQ
Q: Does the Montessori research apply to all ages or just preschool?
The 2025 PNAS study specifically focused on preschool (ages 3–6) in the public school setting. An earlier lottery-based study by Lillard and Else-Quest (2006, Science) found that 12-year-old Montessori students wrote more creative essays with more complex sentences, chose more positive social strategies and reported a stronger sense of community — though they did not differ from peers on standardized reading and math tests. The executive function effects appear most critical in the 3–6 window when the brain’s prefrontal cortex is most rapidly developing.
Q: What age should my child start Montessori for maximum executive function benefit?
The study enrolled children at age 3, which aligns with a critical sensitive period for executive function development. Most Montessori practitioners recommend the 3–6 classroom as the foundational period. Starting at age 4 or 5 may still provide benefits. Whether completing the full three-year cycle is what drives the results is still an open question — the authors note the study was too small to test that, and it did not follow children beyond kindergarten.
Q: Is Montessori good for children with ADHD or attention difficulties?
This is an active area of research. Some studies suggest the self-paced, movement-friendly Montessori environment can be supportive for children with attention challenges. However, this study did not specifically examine neurodivergent populations. Talk to your child’s pediatrician and observe the specific classroom before enrolling.
Q: How do I find a public Montessori school near me?
The National Center for Montessori in the Public Sector (NCMPS) maintains a directory of public Montessori programs in the US. Search “public Montessori [your city/state]” and verify teacher credentials directly with the school.
Q: What’s the difference between AMI and AMS Montessori credentials?
Both are internationally respected. AMI (Association Montessori Internationale, founded by Maria Montessori’s son) emphasizes strict adherence to original Montessori principles. AMS (American Montessori Society) incorporates some adaptations for the American context, including more flexibility on mixed-age groupings. Both require approximately one year of full-time training. Either credential indicates a meaningfully trained teacher.
Products We Recommend
If you’re building Montessori-style executive function practice at home while you evaluate schools, these are genuinely useful:
The Whole-Brain Child — Daniel Siegel & Tina Payne Bryson The clearest explanation of child brain development I’ve read. Siegel’s “name it to tame it” strategy for emotional regulation maps directly onto the self-regulation skills Montessori builds. Required reading.
How to Talk So Little Kids Will Listen — Joanna Faber & Julie King Practical scripts for daily situations that support the same executive function development the PNAS study measured. Not theory — actual phrases you can use tonight.
Lovevery Play Kits — Montessori-Inspired Stage-Based Toys If your child isn’t in a Montessori program yet, Lovevery’s kits bring the material-based, age-specific approach home. The open-ended physical materials support exactly the focused attention practice the research highlights.
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