Childcare : what the science says

Great, so if you were to write a science based, research backed rebuttal to this chapter alone, it would recommend what exactly? No daycare? Daycare in particular family instances at particular ages?

I ask knowing full well I likely won’t be able to meet the ideal, but I personally would prefer to know what that ideal is to attempt to get closer to it.

I know the research here, but I’ve always been reluctant to write about it: everything’s so politicised and parents (understandably) get very upset if they don’t think they’re doing the best by their children. So I promised to DM the commenter. And then this happened…

And more…

Science and Authority

Books on parenting usually do this…

Center Care

There’s a lot more research on center-based daycare than on other childcare options. I’ll go over that first and then talk more briefly about in-home care, etc.. Effects are always measured relative to children staying at home.

Summary of effects

First, here are the effects of 15–30 hrs of daycare a week, broken down by age.

  • For ages 3+, there are few downsides and substantial advantages. Daycare boosts both cognitive skills (literacy and mathematics) and social skills as measured in the first few years at school.
  • For age 2, the findings are more mixed. This is the best age to start in terms of boosting later cognitive skills, but children are more likely to act out and be angry when they reach school.
  • For age 1, childcare may improve cognitive skills a little, though certainly less than starting at age 2. But it also has even larger negative effects on later behavior in school. There is no boost to social skills.
  • For children aged 0–12 months, daycare likely damages cognitive skills and children’s later behavior at school is even worse. There is no boost to social skills.

If there’s one thing you take away from this post, please let it be this: age makes a huge difference.

Compared to 15–30 hours, 30+ hours a week before 4 or so doesn’t give any cognitive benefits but makes children more likely to act out and be angry when they reach school. For children from “middle class and affluent families”, that much time in daycare has about two-thirds the negative effect on behavior of having “a moderately depressed mother”. Children spending long hours in any kind of out-of-home childcare have been found to be three times as likely to have “elevated levels of aggression”.

Age matters. Hours matter. Income matters.

Sources: The effects on cognition and the link between center care and later externalising behavior (“acting out”, etc.) at schoool have been found many times. See e.g. (NICHD, 2002), (NICHD, 2004),(Melhuish, 2004) and (Stein, 2013). (Loeb, 2007) is the best single source, though, as it splits results by age and income, and considers ages 0–5. Its findings about young children are borne out by later studies such as (Fort, 2016), (Kottelenberg, 2014) and (Morrissey, 2010). Over a dozen papers have shown negative effects of non-parental care in the first 12 months; see (Im, 2018) for a review. For differences in outcome by family income, see (Melhuish, 2015) and also (Votruba-Drzal, 2004) for cognitive aspects.

Cognition vs Behavior

Those results might suggest a trade-off between cognitive skills and behavior, but that’s a shaky interpretation for two reasons:

  • Parents likely impact cognitive skills more than daycare, but daycare impacts behavior somewhat more than parents. So e.g. parents can improve children’s literacy by reading to them at home, but it’s much harder to fix behavioral problems caused by daycare.
  • Cognitive boosts probably fade out, although it’s not completely settled; skills needed to regulate behavior persist through life.

Social Skills

The part that I most often see parents get wrong is this: they assume sending young children to daycare will improve their social skills. It doesn’t: the one large study of this finds more time in daycare is linked to poorer social skills in primary school.

From the first textbook on play I had at hand.

Cortisol and Stress

Why does daycare usage affect some children’s behavior years down the line? There’s strong evidence that it relates to children’s stress levels in daycare.

From a meta-analysis of high-quality centers (Vermeer 2006). Note the broken y-axis.


High quality daycare reduces all the negative effects I’ve discussed above, although it doesn’t eliminate them. It also has long-lasting positive effects on educational outcomes. That’s the good news. The bad news is that it’s hard to find; only 10–15% of daycare in the US is high quality, and many child care centers offer “disturbingly low quality programs”.

There are, sadly, very few high quality daycare centers in the US. (Helburn, 1995). Also see (NICHD, 2000) for similar data.

Effect Sizes

Researchers talk about small, medium and large effect sizes. Those are technical terms. Even Cohen, who invented them, warned against using them out of context. Unfortunately, they’re abused all the time to push various agendas to laypeople. I want to try to give you a sense of how large daycare effect sizes are in a way you can understand.

  • Even with the boost from that nutritional program, many children will grow up to be short. (Just, on average, an inch less short than they would have been!) Similarly, even with extensive exposure to daycare, many children will grow up without behavioral problems or later mental health issues. Daycare and the other factors shift the odds; they don’t guarantee bad outcomes.
  • A small shift in the average makes a big difference to the tail. If everyone was an inch taller, there’d be three times as many American men over 6'4". The same applies here: the ‘inch’ of worse behavior caused by long hours in childcare results in triple the number of children with ‘elevated aggression’.
  • Remember that average effects are measured. Some children will be much more affected and some less or not at all. Also remember research shows parents are bad at seeing the behavioral effects of daycare on their own children.

Other forms of childcare

To run a good scientific study of two alternatives, you need a couple of hundred data points in each bracket. It’s (reasonably) feasible to find and engage 200 children in daycare and 200 cared for by their mothers. It’s much harder to round up, say, 200 children cared for by nannies. As a result much of the research compares daycare to maternal care; research on anything else is sparser, so this will be a short section. Here are the key points:

  • All forms of relative care seem to be as good as each other. Mothers, fathers, grandmothers — doesn’t matter. Indeed, there are large studies comparing single fathers and single mothers and the differences are minimal.
  • Time with professional childminders (a.k.a. in-home daycare providers) can cause later behavioral problems, but much less so than daycare centers. Childminders do not however boost cognitive skills of older children as half-days in daycare do. (Usual caveat: such boosts probably fade out, whereas behavioral effects have long-term consequences.)
  • How do nannies (who come into your home) compare to professional childminders (in their own homes)? Research is sparse, but it seems that nannies may cause fewer emotional problems than childminders, and (like childminders) do not give cognitive boosts.

Further Reading

If you want to look into this more, there are a number of general reviews. (Bradley, 2007) and (Philips, 2010) are a bit outdated but short and readable. (Burchinal, 2015) has the more recent work; one thing to watch out for is that although it highlights issues with maternal questionnaires, it doesn’t catch all the papers that rely on them. (Melhuish, 2015) is also good, though be sure you look at the ‘general population’ half rather than the ‘disadvantaged backgrounds’ half. (Jacob, 2009) is a widely cited review of the effects of childcare on behavior. (Sylva, 2010) is a whole book of findings from a large British study.

Universal Childcare

In the first version of this article, I wrote a little about the evidence from economics on universal childcare programs. I was trying hard to keep it short, but that caused misunderstandings. So in more depth:


Quebec implemented universal childcare from birth in 1996. The US NBER summarised the key paper in an article called ‘Canada’s Universal Childcare Hurt Children and Families’. Some quotes (my emphases):

  • The paper picks up something that is specifically happening to preschool children, ramping up from 1996 to 2001. Nothing happens to older children, which makes it unlikely that it’s e.g. the Quebec economy.
  • Quality standards were increased in 1996 as part of the program roll-out. Overall quality was actually pretty bad, but still ‘comparable to the quality of care provided in many other countries’. 25% of the centers were good quality, which is about double the figure for the US.
  • Economists Steven Lehrer and Mike Kottelenberg heard about the results and flat-out didn’t believe them. So they replicated them. Lehrer writes:
From a public draft of Baker et al, 2019. The different lines show show crime rates go up in cohorts with more exposure to the universal childcare system. The lowest solid line is for children who were not exposed to the system.
  • Most strikingly, the crime rate goes up by about 20% when the children who were in daycare become teenagers. That figure seems to shock people, but as far as we can tell it’s real. Here’s a way of looking at it. If I told you crime rates were higher among children who grew up in more deprived families, would you be surprised? Typical daycare centers have some similar characteristics. There’s less attention per child, more noise, people are more stressed, etc.. So you get the same effects on brain development and the long-run consequences of that, including in crime rates.
  • The Quebec program covered ages 0–4; the negative findings were disproportionately driven by the youngest children. Hours seem to be long. And the program looks to have mainly changed the behaviour of advantaged families. So it’s not surprising that the outcome was so bad. (Age matters. Hours matter. Income matters.)


A very recent study looked at a1996 expansion of universal preschool in Boston.

  • The study was only looking at 4-year-olds.
  • Hours were relatively short; at most six hours a day (30 hours a week).
  • The intake was ‘relatively disadvantaged with high shares of non-white and low-income students’.


People talk admiringly about the Scandinavian childcare system, but the research is mixed. (Drugli et al, 2018) find elevated cortisol levels in Norwegian toddlers in childcare; (Berg-Nielsen et al., 2012) note that “sadness, tears and fears may simply be regarded as common and age-appropriate”. (Hårsman, 1984) observed babies in Swedish daycare for five months and reported that 52% of them were “sad and depressed in the day-care setting”.


You didn’t ask about policies, but I’m going to tell you (briefly) anyway, as the only way to make life better for all our children is at the level of society. Feel free to skip this section.

  • You sometimes hear that investing in early childhood has huge returns. (The ‘Heckman Equation’.) That’s specifically true for low income children. It’s based on an analysis of two high-quality interventions (1962 Perry Preschool and 1972 Abecedarian). The 200 or so children in those projects were all poor, and nearly all African American.
  • Hours matter. There’s a big difference between being in a center 8am–6pm (50 hours a week) and being in a center 9am-3pm (30 hours a week).
  • Above all else, age matters. Journalists keep missing this. If you muddle together all the evidence from studies on 12-month-olds and studies on 4-year-olds, it looks like the evidence on childcare is mixed. But that’s a completely wrongheaded thing to do.
  • Parents who need to can still spend the money on professional childcare. But because fewer people will use center care (‘reduced demand’), the cost of center care will go down, so parents using it will end up with cash in hand.
  • For other parents, the money will mean that they, or relatives, are able to look after their babies themselves.


Well, I guess I never answered the question.

Great, so if you were to write a science based, research backed rebuttal to this chapter alone, it would recommend what exactly? No daycare? Daycare in particular family instances at particular ages?

I ask knowing full well I likely won’t be able to meet the ideal, but I personally would prefer to know what that ideal is to attempt to get closer to it.

I hope you now have the information to answer that yourself, because there are a lot of nuances which I’m nervous glossing over. But if you want my own answer, for the average child:

  • The best behavioral and cognitive outcomes come from starting half-days in daycare around 2½. Switching to full days provides no benefits and long days may worsen behavior until around 4.
  • Before 2½, any relative as carer gives the best outcomes. Failing that, nannies are probably better than childminders (in-home daycare) and both are certainly better than daycare centers.
  • All of the negative effects of non-relative childcare are more pronounced for younger children; childcare choices in the first 12 months make the most difference, as children are particularly dependent on their carers then.



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Key science, with sources. Minus bad statistics. Minus shaky methodology. Minus politicisation, left or right.