When I was at school we did twice yearly exams through primary, which enabled us to have a rank in the form, we also had a mark, (out of 200, 100 being the expected from an average ability). This meant that the form could be compared in a weak sort of way with other years. I think things aren't marked as much with "points" in the same way, so ranking would be harder.
From my form 3, went to my secondary where we were put into different forms. Our "ranks" at primary were approximately: 1st, 3rd, 15th (out of 30). When we got our "rank" from our secondary at the end of the first term, we were all 3rd. Thus showing how the forms ranked in ability.
Rank isn't totally useless for a parent though.
NC levels sound great, but how many parents actually have a really strong grip on what is good and what isn't.
I know for my dc we were given at juniors a sort of chart: Expected for year 3 = 2a-3b (or whatever, I can't remember). This meant that some of the people whose dc had got 3b across the board thought they had a genius on their hands. But what they didn't know was that for year 3 they assessed up to 4c. When the maths sets across the forms (big school entry) were given there were some very indignant parents. If they had been told 3b/15th in the form, it would have not been so much of a shock to find there were children better.
But I think the op wanting to know to check her dc are in the top handful, is a bit sad really. I mean everyone would like to know their dc are popular, clever and the mainstay of the form
. But to be asking to check that, seems to be putting a bit too much emphasis on that for a year R. And just because the school is requiring improvement, it doesn't mean there aren't some very bright children there.