In an ideal world, all teachers would be dedicated, hardworking, articulate, not overworked and able to provide comprehensive feedback to parents and DC on how they are doing relative to where they should ideally be and whether they are working to their potential/what they need to work on.
Unfortunately that's not the system we have and whilst most teachers fit most of the criteria above (apart from not being overworked and having the time for comprehensive feedback), some don't and the system also doesn't really work well ime.
I preferred the old style reports where a teacher would write freeform about how your child was doing rather than a bunch of paragraphs selected from a computer database that told me what they'd been covering.
Teachers are human the same as the rest of us and some do a brilliant job, some do a decent job, some do an adequate job and some just shouldn't be in teaching. I've come across all types. My DC had one teacher in primary that just basically coasted through the year and didn't seem to progress any children, this was in the 5-14 times and none of the children I'm aware off in her class ever seemed to move up any levels, the excuse being that although they'd progressed (they hadn't) they still weren't quite ready for the next level yet. Funnily was also the only teacher in primary not to say that Dss had been a joy to teach. Told one DS that he was wrong about when his birthday was so he didn't get a pencil from the headmistress - he still complains about that! :o Other teachers have energised and enthused and encouraged and I'm really thankful for them. Interestingly, the primary teacher that most of the DC in school were scared of and was supposed to be very strict was one of the best and most loved of all their primary teachers. She was so passionate and enthusiastic and my DC ended up not scared very quickly as to be fair I think she was less strict than me!
Anyway, the point i suppose is that we shouldn't need testing to demonstrate how DC are doing but I can totally see why parents want it and also why it's not necessarily a good thing. Splinters in my arse now from sitting on the fence.