I think there are several really important points here that speak to the tension that can develop between home and school.
Parents naturally want to understand how their child is doing. I think we can all agree that happens and shouldn't be surprised.
Some parents are expressing it in terms of the class - because they know some of the children and have a sense of their ability and can then gauge where the DC is in comparison to children they actually know. I think what parents don't understand is this is unfair to all the children and as mrz rightly pointed out each year the attainment of a class (say Y4) can vary - one year a Y4 class can be struggling and the next year a Y4 class can be high fliers. So as many have suggested - it is best to consider your child against NC Levels for SATS (L1 - L3 KS1 and L1 - L5+ KS2).
Diddee I can understand that these prepared statements of targets seem very dry and not particularly helpful - but the APP system of breaking down learning into several components to achieve a secure level (say 3a for example) does mean that areas of weakness can be identified and explained to the parent.
However as a parent I agree with many comments that teachers often appear to speak vaguely about things generally. I certainly would love to see more class work coming home so that I could have a feel for what is being taught over the week - but our school says everything has to be saved for Ofsted. (is this true teachers out there?)
One thing that does strike me as unfortunate is that when parents are genuinely concerned about how their child is progressing and asking those tough questions and querying why x or y isn't happening at parent/ teacher meetings, after school, etc... and raising why x doesn't happen here when it is in place down the road at a nearby school... this type of parent is almost always labelled 'pushy' by teachers (which let's face it is pretty negative) - yet in the same breath schools are constantly asking for parental support and involvement.
The hugely depressing documentary How the West Went Bust by Robert Peston (still on BBC iplayer: episode 2 about education - www.bbc.co.uk/iplayer/episode/b018jshh/The_Partys_Over_How_the_West_Went_Bust_Episode_2/) is worth viewing - as parents & as educators - because he quite clearly believes we are losing the economic battle here in the UK because we are not achieving or competing educationally.