Good to see some scientific backing for what Margaret McMillan was advocating a century ago:
https://en.wikipedia.org/wiki/Margaret_McMillan
She also though that open-air schools were a good idea, and that if the kids were properly fed and slept they'd do more. All very likely correct.
Politicians like to talk about going back to the three R's, as if there was too much play. Presumably it's capitalist thinking behind that. Everybody's supposed to maximise their output, mustn't "waste time." But people aren't simple machines like that, so it doesn't work out very well.