Have you noticed?
"The latter variations are likely to have the greatest impact on the variability of a school's key stage tests where cohort sizes are small . . . For very small cohorts - below 20 - inspectors should place very little weight on the key stage test results for one year."
In my county, more than a third of primary schools have 20 pupils or fewer per year group. Even for substantially larger year groups, the guidance urges caution. A change of 1 per cent is said to be the minimum significant change for a cohort of 60.
Even a 15 per cent variation in a group of this size requires other supporting evidence before it can be considered as a firm indicator of changes in the standard of achievement of the school. Only about a dozen schools in my county have a cohort size of more than 6O pupils.
So why are these unreliable figures used to compile annual league tables?