The Society of Headmasters and Headmistresses of Independent Schools want children to be included in the tables only after they have taken their GCSEs.
Anomalies arise because the Department for Education and Employment bases its calculations for schools' performance on the number of 15-year-olds on roll. Independent schools are more flexible than most state schools in allocating children to the year appropriate to their needs, with the result that pupils who take their GCSEs later are not counted in the tables that many newspapers have published this week. And because they have appeared as 15-year-olds the previous year they have already been listed as non-achievers, says the society.
A survey of 360 member schools suggested that four out of five would be shown as having worse results than they achieved and nearly a quarter with 10 per cent lower than the true figure. One school appeared as 27 per cent below its real performance. On average, schools in the society had the important "five or more GCSE A-C grades" measure about six per cent lower than the real figure.
Russell Buley, head of Shebbear College, Devon, who helped to carry out the survey, said it was nonsense to classify children who had not been tested as total failures. "They should not be included until they have taken GCSE. Parents are entitled to accurate, not misleading, information."
The society is particularly incensed that newspapers ignored an optional section of league tables, introduced by the DFEE last year under pressure from independent schools, which counted total numbers in Year 11 because it included data on only a third of state schools.
This week's tables show that all the pupils in the top 50 independent schools achieved five A* to C-grades at GCSE. Manchester Grammar School improved on its 99 per cent performance last year with all 201 boys achieving grades in the top range. It was also joint first in the ranking of all types of school.
Aylesbury High School for girls got all 181 entrants through and improved its rating from fourth in the overall national league to joint first. Three other independent schools shared the best individual Universities and Colleges Admissions System score, at an average for their pupils of 35.9: King Edward V1 High School for Girls, Birmingham (top last year), King Edward's School (boys), Birmingham and St Swithun's School (girls), Winchester.