It’s theoretically means schools don’t need to teach new content while they are closed, I think the rationale is that those who can’t access online learning would be disadvantaged so it’s best if everyone stands still. Schools are supposed to only be setting revision type activities to keep kids ticking over.
Meanwhile, the private schools realised parents weren’t going to pay for a few revision worksheets and carried on teaching the curriculum as normal, with 99% of children able to access the online learning they set. And so the gap widens.
But its fine, the kids will all catch up when they go back to school, even if that’s 6 months or so after they stopped going. Presumably the virus means children will learn twice as much as normal when they return to school to make up for lost time.