Ds has just started Year 7 and spent one morning this week doing tests - he said they were a bit like the 11+ (VR, NVR, Maths). Is it to give them a baseline level for them to work from? If so, why bother with Year 6 SATs? Do we get to know how they did?
Our line at my school is that quite often the data we receive from primary schools is incomplete (for this read, "we don't trust it because we know that our feeder primaries cheat") We test their reading, writing and spelling in the English dept and I assume maths do their own version.
We also do cognitive ability tests primarily to determine our GaTs but also so we can spot any kids that have very low scores and give them support.
I always tell parents exactly how their kids did; if your school don't tell you then I'd ask at parent's evening.