Kindergarten/Preschool research

In considering the value of what the Chinese call Kindergarten (age 3 4 5) and Americans calls Preschool (typically age 3, 4…age 5 is kindergarten), I want to jot down the research I’m aware of.

It’s all from USA. Need to add foreign research later.

And I’m focusing on studies that are empirically strong.


A common refrain in USA is that “high quality pre-school is proven” to have large beneficial effect on kids.

But that’s something of a shell-game.

It comes from 2 very small fifty year old studies. From Scott Alexander:

…Early RCTs of intensive “wrap-around” preschools like the Perry Preschool Program and the Abecedarians found that graduates of those programs went on to have markedly better adult outcomes, including higher school graduation rates, more college attendance, less crime, and better jobs.

But these studies were done in the 60s, before people invented being responsible, and had kind of haphazard randomization and followup. They were also small sample sizes, and from programs that were more intense than any of the scaled-up versions that replaced them.

So those small programs “worked.” Probably.

But when folks have tried to scale up those programs, to serve many kids, the results have been disappointing.

Modern scaled-up preschools like Head Start would love to be able to claim the mantle (of Perry and Abecedarian) and boast similar results.

But the only good RCT of Head Start, the HSIS study, is still in its first few years. It’s confirmed that Head Start test score gains fade out. But it hasn’t been long enough to study whether there are later effects on life outcomes. We can expect those results in ten years or so.

(From previous research)…Good randomized controlled trials have shown that preschools do not improve test scores in a lasting way. Sometimes test scores go up a little bit, but these effects disappear after a year or two of regular schooling.

And unfortunately there’s a new disappointing study from Tennessee which actually found some negative impacts of preschool for poor kids. They did better at age 5, but a little worse by age 8.


This article in the Atlantic

Research suggests that preschool only benefits children from these disadvantaged families (in particular, families that are below the poverty line, whose mothers are uneducated, or who are racial minorities). This could be because preschool acts as a kind of “equalizer,” ensuring that for at least a few hours a day, these kids get the same high-quality interaction with adults as more advantaged children do, which helps to even the developmental playing field.

For instance, in a study published last year, University of Texas psychologist Elliot Tucker-Drob assessed a number of different characteristics in a group of more than 600 pairs of twins. He looked at the scores the children got at age 2 on tests of mental ability; whether or not they went to preschool; how “stimulating” their mothers’ interactions were with them; their socio-economic status and race; and finally, how well they scored on reading and math tests at age 5.

…A hell of a lot of math later, Tucker-Drob reported that the home environments of children who do not attend preschool have a much larger influence on kindergarten academic ability than do the home environments of preschoolers.

In other words, a bad home situation becomes a much smaller problem when your kid goes to preschool; when you have a good home environment, preschool doesn’t really matter.

In our family’s experience, I don’t think preschool helped create academic gains. They got much more of that from Grandma Jean and Angela, their nanny. But I suspect they got some socialization gains from pre-school, particularly our son.

And for Pru, it was definitely nice on her 2 days off each week to have the mornings for herself (while kids were in pre-school til noon), and the kids (and me!) benefited from all that.

Some new research does suggest that certain Montessori schools could provide an academic edge over conventional preschools, even among advantaged children. Research on Montessori is overall a mixed bag—some research suggests kids do better in them, while other research suggests the opposite.

So last year, Angeline Lillard, a developmental psychologist at the University of Virginia, conducted a study to try to tease out the truth. Montessori schools can be parsed into two types: classical Montessori and what Lillard calls “supplemented” Montessori.

The classical approach strictly abides by the founder’s rules, only allowing certain types of materials in the classroom and grouping kids of different ages together. Supplemented Montessori, which is far more common in the United States, typically separates children according to age and augments traditional tool-based Montessori learning with activities like pretend play and direct instruction.

When Lillard compared the test scores of children from advantaged families who spent a school year in conventional preschools with those who spent a year in the two types of Montessori schools, she found that children in the classical Montessori programs fared much better than both the other groups. At the end of the school year, they exhibited better working memory, planning, reading, and vocabulary skills, and they displayed a better understanding of fairness and willingness to share.

So that’s good.

But no one yet knows whether these advantages last, and indeed, some research suggests that the academic “edge” some kids get from preschool fades over time.

(There are similar arguments over the lasting effects of Head Start; programs across the country differ drastically, so it’s hard to tell why some seem to help and some don’t.)

I wonder if Lillard has done a follow-up study.


It seems like a good time in this blog to get back to the subject of Head Start. The thing is:

– This research only applies to poor kids.

– So it’s only moderately useful to guess how it might apply to middle class kids.

– That said, there is SO much research from Head Start. So you need to be familiar with it to get any traction in this area.

Kelsey Piper recently assembled the research in Vox:

Her take:

There’s a bizarre-seeming paradox sitting at the heart of research into early childhood education.

On the one hand, there’s a sizable body of research suggesting that kids who go through intensive education at the ages of 3 and 4 don’t really come out ahead in terms of academic abilities. By kindergarten much of their advantage has receded, and by second grade researchers typically can’t detect it at all.

On the other hand, there’s an equally substantive body of research suggesting that early childhood education produces a profound, lifelong advantage. Kids who enter intensive preschool programs are less likely to be arrested, more likely to graduate, and less likely to struggle with substance abuse as adults. One study with a followup when the students were in their mid-30s found that they were likelier to have eventually attended and completed college.

This is an area where research is fiercely debated — and really important. In 2017, the US spent $9 billion on Head Start, the flagship early childhood education program launched in the 1970s. If one set of studies is wrong, that has profound implications for how we should be spending that money instead.

Here’s an explanation that makes sense of all the research: The benefits of early childhood education aren’t coming from the academic skills they teach students. Early childhood education helps because it’s reliable daycare.

Get that?

Her argument: It’s not so much helping the kids learn stuff or get socialized to school.

It allows poor parents to get or keep better jobs. Maybe it also gives Grandma a break so she’s nicer to her grandkids when she watches them in the afternoons (instead of having to watch them mornings AND afternoons).

I find this theory interesting/plausible.

Still, there’s Stanford’s Raj Chetty, who showed that a good kindergarten teacher (age 5 in USA context) actually has noticeable impact on a kid’s earnings many years later!

So that would suggest “good” kindergarten teaching does matter. It’s not just that “any decent childcare frees up Mom.”

Scott Alexander offers two good summaries of all this stuff.

Part 1 here (agreeing with Piper, above).

Part 2 here (sort of reversing himself, becoming more skeptical).



I’m not yet aware of any studies comparing the difference between “good” and “bad” kindergartens.

That is, with charter schools, we know there’s a bell curve distribution of them. Of quality! Like with most things in life.

So while it’s useful to know the average effect of “charter school,” to me it’s far more interesting to understand the wide variation among charter schools, and in particular then to zoom in on the outliers.

My guess is that the same is true with kindergartens. If Chetty is right, that a good kindergarten teacher “matters,” then presumably if you can build a kindergarten with several good teachers, you might create a significant lifetime positive effect for kids.

Some kindergarten directors, like with charters, are better at:

a. hiring good teachers (and avoiding bad ones)

b. providing better curriculum and “instructional systems” (like parent-teacher communication)

c. onboarding, coaching, training, and appreciating their teachers

So the good kindergartens might have a nice positive effect, the bad ones might have a negative effect, and together it’s no effect…but as a parent what happens if you hit the jackpot and get a good one?

That school quality research, to my knowledge, has not been done. (I need to dig deeper here).

I would love to see an empirical study of, say, Bright Horizons (well-run chain of 900 pre-schools serving middle class and upper middle class families).

Do they outperform typical preschools, the way KIPP and Uncommon and Success outperform typical charter schools? I’d guess: yes.

If I’m able to help start a kindergarten in China, I wonder if I can find a doctoral student to help us assess our impact.

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