This is a pretty good summary of the research on daycare effectiveness. It is a Much More Than You Wanted To Know-style post from a science blogger criticalscience who has some interesting posts on Medium.

TL;DR:

  • Adverse effects on children younger than three years old.
  • The effect is worse the younger the children are.
  • The effect is stronger for longer hours.
  • The effect is weaker CORRECTION: worse for children from socio-economically better-off families.
  • Nannies are OK.

Childcare : what the science says

4 comments, sorted by Click to highlight new comments since: Today at 4:16 PM
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This is great, thank you for the link! My 16-month-old niece recently started daycare and that's seemed like a shame to me since she was thriving on tons of one-on-one attention (being with a rotation of loving relatives from 7am to 5pm on weekdays, and parents the rest of the time). I think her parents made the switch because they want her to be socialized but I now see that that's not a thing; maybe I can get them to pull her back out and wait until she's older! :D

I think socialization may play a positive role later on in school, but for toddlers in daycare, the results are indeed very clearly negative.

That's an awesome text, thanks!

The 4th point in your TL;DR seems wrong to me, though. What I understand from the text (in relation to socio-economic status of the family) is that daycare may even be good for babies of worse-off families even when the babies are really young, but that it is clearly negative for babies of better-off families until they are 3+.

You are correct. The relevant section is this (emphasis theirs):

All of that is for an average income family. Low-income children benefit from starting earlier, and high-income children from starting later. (It’s likely not just actual income that matters, but socioeconomic factors — but income is easy to measure objectively so researchers measure it.) The most deprived children can actually benefit from starting as 1-year-olds.

I correct the TL;DR.