Somewhat surprised at people saying an all-over lace dress is too casual - I'd have said it was a bit too fancy for daywear except a dressy wedding.
Its a just school dinner dance, fgs, not a 'ball'!
I bet a lot of the blokes will be wearing lounge suite and some sort of normal tie. Its a lovely dress, a bit unusual, looks easy to wear confidently ... honestly, it'll look way classier than some ostensibly more 'formal' frocks ... and at a school event overdressed is much worse than a little underdressed.
Dark shoes definitely though for evening. Certainly don't choose spindly ones if (like me) you can't walk in the damn things.