Well that's already not true because in areas outside lockdown it's now up to heads
It's always been up to heads though? Before the change they said it was unnecessary and not recommended but it wasn't banned. Heads could (and were) encouraging masks. Now it's totally up for interpretation. Heads will probably still make the same decision they had planned to make (or have already made) before the u-turn.
In the school where I work the guidance it's been, 'wear a mask if you'd like to but don't feel you need to' since the first communication mid July.