I think the post above from Roadlesstravelled does make a lot of sense - but....
I would add at primary children are facing a prevailing attitude that 'all the school need do is get them to NC L4 standard'.
I've had multiple conversations with teachers at our DDs school about how NC L4 is what they work to (and no higher). Thus DD1's Y6 cohort of 30 pupils is now split into two groups (one with a KS1 teacher who are secure NC L4/L5 and one with the Y6 teacher who are really struggling to get to NC L4 and the school is throwing everything at them in one last ditch effort to get that all important NC L4 on KS2 SATs).
They didn't listen when I said:
Isn't it odd that there has never been maths homework in Y1?
Isn't it odd that so far there's no numbers on maths homework in KS1 (YR/ Y1/ into mid-1st term Y2)?
I think it is a mistake to abandon multiplication table homework?
Why aren't library books coming home?
Why aren't guided reading books coming home any more?
etc....
I fear they're now reaping what they sowed.
I suspect our school relies heavily on a significant component of each cohort prepping for the 11+ and garnering them easily earned NC L5s.
But back to the topic...
What is disturbing about KS2 SATs feeding into senior schools is that these pigeon hole children's access to learning/ teaching. However, I am aware of some senior schools almost instantly re-testing children and not taking a huge amount of notice of the KS2 SATs - basically starting from scratch with every child.
Like anything - it totally depends on the individuals (the teachers) involved - and the 'ethos' of the management of a school.
I sincerely hope there are schools out there that accept there can be late bloomers and sudden, swift improvements when finally a child just gets it (or responds well to a great teacher who makes a subject fun to learn). I hope there are schools that recognise improvement early, encourage it and move children up to higher ability forms in KS3. But I also know that there are schools here where you come in, are put into a certain form and there you stay for the duration.