Apparently it is hard to understand (the column that shows 'value added'), and also it assumes that pupils who start off weaker can't attain highly.
Surely this is just going to further disadvantage schools that have a weaker intake than schools in so called 'good areas'? You simply can't compare schools from 'good areas' with some schools in terribly deprived areas - for starters, there is often a massive job teaching english to a lot of the students!
It will just render the league tables useless, but give the government ammunition to get the weaker schools taken over.