Most schools allow you to take two weeks (ten school days) WITH the prior permission of the Headteacher. In our school (primary) we discourage children taking holidays before and during SATs. If you don't get permission you can end up having to pay a fine of up to �200.
generally the SATs are always held around the first week in May, but still check. They have to get them over with before the GCSE's start that's why they tend to have them then.
My 14 yr old son did his Sats last week (his sister's doing hers this week!). We always go away end of May for 2 weeks and for the last 3 yrs have taken the oldest out of high school as he only gets 1 week and school have been ok about it. Won't be doing it next year as he starts his GCSE year.