Sheffield’s final GCSE pass rate for 2014 is expected to show a sharp downturn - with changes designed to make the courses tougher having a major impact on many schools.
After years of progress, the number of students passing five subjects at grades A*-C is expected to fall by at least three per cent, putting the city even further behind the national pass rate.
Final figures will not be revealed until January when the Government publishes national performance tables.
But research carried out by The Star has discovered results at schools which previously refused to reveal how they had fared.
And it has emerged that other schools did not publish pass rates which will appear in the league tables - instead using the old system which placed them in a more favourable light.
It has been revealed that Chaucer School in Parson Cross had the worst pass rate in the city, 32 per cent, down nine per cent, despite being part of an academy chain headed by the successful Tapton School.
King Ecgbert School in Dore also initially declined to reveal its pass rate of 66 per cent, down from 70 in 2013 and 80 per cent in 2012.
Schools expected to have done worse than first thought include Meadowhead and Stocksbridge High.
Analysts at Sheffield Council do not yet have the complete picture as academies do not have to report their results to the local authority.
But it is clear schools in less well off areas have been worst affected, especially in GCSE English.
One head said: “Students at high performing schools who would have received A or B passes may have got lower grades but still achieved five A*-Cs.
“But those at mid-table schools expecting B or Cs may instead have got a D - putting their school’s results through the floor.”