Pupils were to be ranked based on overall performance. A single mock shouldn't have affected this.
This is absolutely right
Ranking systems for performance management are infamously inaccurate and also regularly suffer from institutional bias. I'd be interested to see a demographic breakdown of the downgrades.
Ranking systems used to form part of performance management for most ivy league companies. We spend sodding days trying to fairly rank the people in our practices and then defend them in roll ups. Its a right old game. This is because the bottom 5/10/15% were likely to leave in a "progress or leave" career model.
However even in companies using this method, typically someone would need to be "bottom end" twice to go due to the arbitrary nature of many of the comparisons.
Companies moved away from this method because its frankly bad and identifying genuine poor performance and legitimate comparison.
Asking people not used to doing this finegrained comparison is asking for trouble frankly. Its extremely difficult to do fairly without being blinded by "star moments" (like the mock result) or "star personalities".
Mind you even this doesn't explain results in a large school lower than any of their previous three year results.
The whole thing is fiasco and I'm sick of teachers being blamed for a government created mess. Williams for this nonsense with ofqual and Gove for getting rid of any moderated alternate inputs to the process.