I'm reading Nurture Shock by Po Bronson & Ashley Merryman. Several things in the book, esp. the chapter on "Tools of the Mind", an intriguing education program, suggest that our education of young children not only isn't very good even when evaluated using tests that the curriculum was designed for, it's worse than just letting kids play. (My analogy and interpretation—don't blame this on the Tools people—is that conventional education may be like a Soviet five-year plan, trying to force children to acquire skills & knowledge that they would have been motivated to learn on their own if there weren't a school, and that early education shouldn't focus entirely on teaching specific facts, but also on teaching how to think, form abstractions, and control impulses.)

Say they're going to play fireman. The Tools teacher teaches the kids about what firemen do and what happens in a fire, and gives the kids different roles to play, then lets them play. They teach facts not because the facts are important, but to make the play session longer and more complicated.  Tools does well in increasing test scores, but even better at reducing disruptive behavior. [1]

Tools has a variety of computer games that are designed to get kids to exercise particular cognitive skills, like focusing on something while being aware of background events. But the games often sound like more-boring ways of teaching kids the same things that video-games teach them.

Tools did no better than the existing curriculum on certain metrics in a recent larger study. But it didn't perform worse, either.

The first study you do with any biological intervention is to compare the intervention to a control group that has no intervention. But in education, AFAIK no one has ever done this. Everyone uses the existing curriculum as the control.

Whatever country you're in, what metrics do you use, and what evidence do you have that your schools are better than nothing at all?

There may be some things that you need to sit kids down and force them to learn—say, arithmetic, math, and typing—but I kinda doubt it's more than 20% of the grade school curriculum. I spent a lot of time practicing penmanship, futilely trying to memorizing the capitals and chief exports of all fifty states, and studying the history of Thanksgiving and the American Revolution over and over again.[2] We could have a short-hours classroom hours control group, where kids spend a few hours a day learning those few facts they need to know, and the rest of the time playing.

ADDED: There is one kind of control--kids who've not gone to pre-school vs. kids who went to pre-school, or who went to Head Start.

[1] I fear somebody is going to complain that disruptive behavior is what we need to teach children so they can innovate and question authority. Open to discussion, but if it worked that way, we'd be overwhelmed with innovators and independent thinkers today.

[2] I actually learned the names of all the states from a song, and learned where they are from a jigsaw puzzle.