COVID Kindergarten is worthless.
My youngest is in first grade now, and is about the most eager-to-please and attentive child you'll ever find (haha, not the older two). But when he's been remote it's been only barely viable...
"Kindergarten" in many cases means something as simple as "human contact instead of bad TV" and "difficult nutrition for the day".
Correlation usually doesn't indicate causation.
Head Start was a lot more than just early education. It was social services, nutrition, mental health services, and even the employment of some parents of the Head Start children. I should be clear that I do not mean to claim the total absence of benefits of kindergarten. I was exaggerating. The position I will stake is that I believe the benefits are likely very minor, even outside of COVID, and especially for affluent children.
That was a good use of our time.
Well designed studies find ways to exploit the enrollment structures. E.g. you let a randomized group of n kids on the wait list who wouldn't end up with services jump the wait list and compare them to n kids stuck on the wait list. Or you randomize half the kids you help to half-day and the other half to full day.
What you describe shows up in "benefits" of various charter school structures. The charter school kids do better than the kids in comparison schools... but if you compare the charter school kids who won the enrollment lottery to those not offered admission, they usually don't look better.
I think this is taking "correlation doesn't always prove causation" a few steps too far, right off a cliff. There are difficulties with reasoning from correlation, but saying it "usually doesn't" indicate correlation is too bold, especially in experiments where confounders have been controlled for. [1]
[1] (And don't get me started with the semi-clever types who ask if this or that variable has been controlled for when the study or the article about the study explicitly says it has. Save us all from halfwits trying to teach experienced researchers their business.)
This is specifically called "shallow dismissal" in the HN rules (used to be "middle-brow dismissal"). Basically this is when you don't read the article and reply with something that sounds smart and applies in the general situation, but not here because the authors knew that too.
I don't plan to "teach" my infant anything till he is 5 or 6. Is this a bad plan?
Which isn't true (you learn languages earlier than that) but I wonder what things it is true for.
You'll teach him to hold your hand when crossing roads, not running out in front of cars. You'll teach him the way you walk to the local shops and back, you'll teach him that kicking you in the crotch is bad, and that he should say "sorry" and not do it again.
You'll probably hang out with neighbours and teach him how to share toys and not fight over them.
All that kind of stuff matters, and is important.
We started taking our child to kindergarden in Finland when he was 1, he'll be going there until he starts proper-school at 7. Mostly they play, draw, listen to stories, sing etc. It's not academic in any sense, but he still learns.
Probably the most important thing he learns is to get dressed and be social with other children of a similar age. He has friends he likes, people he doesn't like, and often these change over a period of weeks/months.
I fully expect he'll be able to read in one/two languages by the time he starts school. We read to him every night, and usually I stop and say the "fox in ?" and point to the word - half the time he'll say the right word, half the time he'll be like "I don't know that word". At first I though he'd memorized the dialog, but when I switch to a new book he's never seen before he still recognizes simple words like "cat", "dog", "hat", "car", etc.
I don't think I'm teaching him to read, we rarely sit down and do anything for more than a few minutes, but he's picked up a lot of things. Like one day he said "That tram is 10", and now he knows about tram-routes within the city "This tram goes to the library", "This tram goes to the swimming pool".
One thing I do when the weather is nice is say "We need to buy cake, where is the cake shop?" He says "go left", "go straight", "go right" and gives directions which we follow. Sometimes he's either confused, or perverse, and sends us in the wrong direction. But that's OK, nice days are worth wasting. But with all that normal stuff we're teaching him stuff, whether it is academic or not.