Ok, so I am not British so find a lot of things perplexing!!
But I just find the while idea of testing 7 year olds a bit pointless and also have concerns that at such an early stage judgments may be made about their ability - because really, at 7 children are at many different stages of development. To cite an example, my dd didn't get reading at all in reception. She slowly started getting it in year 1 and then this year, in year 2, she has really flown through all the levels and is now a great reader at lime level. Her maths is ok, but she is just starting to get it, and I hate the idea of someone making a judgment about it.