If done right ( a huge qualifier) this is actually a far better way to teach then the one-size-fits-all way that they are doing it now.
Not necessarily. This could mean 10 and 11 year olds in a class with 7 and 8 year olds. Too much of an age discrepancy.
It makes sense to me, but I worry about young girls in class with older boys (and other issues involving older kids with younger kids). If everyone was well behaved etc it wouldn’t be an issue (it used to be the norm) but these days....I saw plenty when I was teaching HS, 20 year old boys in freshman classes, hitting on the 14 year old girls.