Staff development day used as revision day - can they enforce this at short notice?

[dizzydance]

Up until now we have been told that the new school term starts on Tueday 8th April with Mon 7th being staff development day.
Today ds1 who is in yr9 and doing sats in may bought home one of those letters with all of next terms dates on it.
On Mon 7th April it states 'Staff training day' ( Yr9 revision day, school closed to all pupils with the exclusion of yr9).
This is the first we have heard of it and surely they can't do this at such short notice. 2 of dss friends don't come back from abroad til the Sunday night, thinking they had the Monday off to recover.
Would you read this as compulsary that they had to go to school a day extra than the rest of the school? Or are they doing it in the hope that they will turn up as if it was stated it was compulsary not many would go.
Normally we get important letters through the post? No good ringing them, they are useless, all you ever get is voicemail.

Sorry, I meant if it was stated it was not compulsary.

I think you have to ring them for this...the students and you should have been made aware before now that this is a revision day - and what are they revising for anyway? Does the school have a website you could look at for more info as well?

If people have booked holidays, and this hasn't been made explicit earlier, then I would not go in. Schools realise that people have to plan lives well in advance, so should not be springing this on you at such short notice.

Thanks. Found out today the revision is for their SATs in May. And it isn't compulsary, parents have to sign a form to give permission. (my ds didn't even bring his home, only found out from someone else). Apparently only about 10 are going in so far,out of about 100 pupils.