I think it's important to note that that study was conducted in May - at which point children had realistically had, at most, half a term at home. It may well be different now.
Of course, school is anxiety inducing for some; my DD is one. And this comment makes sense too -
" Those with the lowest levels of well-being pre-pandemic benefited most, with their scores increasing by 14 per cent compared to no increase in those with average to above average well-being.".
Essentially - those most anxious about school felt the best when it closed. Not really news.
The bigger issue is what can we practically do to alleviate anxieties going forward?