HEADTEACHERS this week called on the Government to scrap its "thoroughly inadequate" system for calculating how effective schools are at improving exam performance.
School inspectors currently judge a school by comparing its exam results with others which have similar levels of pupils on free school meals.
But the Secondary Heads Association has argued that this is misleading to parents and heads, as schools with the same free school meal levels may have pupils with very different ability levels.
Instead, the association called for national tests for secondary entrants.
Schools could then simply be judged on how much they improved results between the ages of 11 and 16.
Tony Neal, the association's vice-president-elect, said that the free school meals approach had been discredited by research, published in February, that the Office for Standards in Education itself had funded.
The study, led by Harvey Goldstein of London University, found that comparing the results of schools with similar free-meal levels was only barely superior to comparing them with any other school as a measure of school effectiveness.
OFSTED said that it accepted that the free meals measure, which it merely implemented for the Government, was flawed. Inspection reports and annual performance and asessment information to schools now came with a warning of the scheme's limitations.
Despite this, the "flawed" measure is currently used to give schools a grade of A to E in published inspection reports and is being used in performance pay assessments and the Government's new teacher-achievement awards.
Mr Neal said: "That means that OFSTED has no valid way of judging a school's examination results."
He said that his own school, De Aston comprehensive, in Market Rasen, Lincolnshire, had scored an E grade for pupils' GCSE performance compared to how many of them were on free school meals.
But on another measure, comparing pupils' performance at age 14 with that at GCSE, it had scored an A.
A Department for Education and Employment spokesman said that the Government would be introducing a more sophisticated "value-added" measure "within the next few years".
The new system would assess a pupil's performance in key stage 2 tests at age 11, and compare that to their GCSE results at age 16.
Because data collection only began in 1998 for children aged 11, it would be three years before they took their GCSEs and the first comparisons could be made.
The spokesman added that although the Government recognised the potential importance of the new measure to schools and parents, it could not introduce it until it was confident that the information was "fair and accurate".