"It is now possible to use the Department for Education's official school census data, completed in January each year, to track the size of individual year groups in 2,785 state schools across England over the years 2010-13. The January census data is particularly crucial for schools in relation to pupils who turn 16 during the academic year, as the number recorded as on the roll at this time is the number whose results are counted against the school in league tables." Two of England's largest academy chains, the Harris Federation and Oasis Community Learning, have several schools each on the list of those whose 2013 GCSE year group shrank the most over the period 2010-2013, and especially during 2012-13. At Harris academy South Norwood, in south London, pupil numbers in the year group that took GCSEs last summer dropped by 22% between the time they were 12- to 13-year-olds and last January, with the year group's roll falling from 197 in January 2012 to 169 a year later, in the lead-up to GCSEs. Overall, six Harris academies feature in the list of the 50 schools with the largest drop in pupil numbers for the 2013 GCSE year group between 2010 and 2013, with all shrinking in size by at least 10% " www.theguardian.com