A section from this document states:
“From the academic year 2015-16, we will move from an absolute measure of progress (i.e. two levels of progress required between KS1 and KS2) to a relative measure. At the same time, KS2 test outcomes will be reported as a scaled score, where the expected score is 100. Pupil progress will be determined in relation to the average progress made by pupils with the same baseline (i.e. the same KS1 average point score). For example, if a pupil had an APS of 19 at KS1, we will calculate the average scaled score in the KS2 tests for all pupils with an APS of 19 and see whether the pupil in question achieved a higher or lower scaled score than that average The exact methodology of how this will be reported is still to be determined.
New performance descriptors will be published (in draft) in autumn 2014 which will inform statutory teacher assessment at the end of key stage 1 and 2 in summer 2016. Final versions will be published by September 2015.”