I'm a teacher, a Union rep, & very much against SATs.
I've got no problem with testing kids, actually. Although there are some subjects, & some skills, where you'll get a better picture of what's going on by looking over a range of work than by a traditional 'test'. But yes, there's definitely a place for them.
The Year 9 SATs were bad tests. They didn't provide reliable results (snapshot performance, untrained/non-specialist examiners). They didn't provide useful results (if I'm setting students in 8 groups, I'd want a little more info than a raw level 'below 4' to '7', actually. So obviously it's done on teacher appraisal). Above all, they were crap tests because they meant we spent the whole of year 9 teaching 'how to do SATs papers'.
A specialist skill, frankly, which had naff all to do with teaching English (I don't pretend to speak for Maths & Science).
The year 6 SATs are the subject of this boycott.
I teach two year 7 groups this year. The SATs-based information I have on them is of pretty minimal value. I've got one 'set 1' (all level 5s) & one 'set 2' (level 4s mostly, the odd 5 & a couple of 3s who did much better in Maths & Science KS 2 SATs).
Honestly, I could've told you by November who'd be in what set in year 8. Their SATs results are the last thing I'd look at.
Total waste of everyone's time.