School pupils are being let down by an exam system which is facing a "perfect storm of both decreasing public confidence and increasing pressure", the head of a leading public school is expected to say today.
Chris King, of Leicester Grammar School, will say a lack of full accountability by exam boards, an inadequate examiner workforce, a "confusing and byzantine appeals process" along with ruthless behaviour by some universities is all contributing to the problem.
Mr King will warn the Headmasters' and Headmistresses' Conference (HMC) that the "current situation is untenable".
"We are facing a perfect storm, of both decreasing public confidence and increasing pressure in the system, as the greater emphasis on end of year exams creates even more work for examiners over the summer," he will say.
Mr King, who is making his inaugural speech as chairman of HMC, will tell the gathering of 275 heads of the UK's leading independent schools he wants to see wide scale and urgent reform to benefit young people in all types of schools.
He will say the "cottage industry" exam marking system is not fit for purpose, and has led to 414,000 exam marks being challenged last year, with a "shocking" 77,450 GCSE and A-level grades being revised - a 42% increase on 2013.
While these figures are very high, he will also say that they potentially mask the true extent of the problem as some state schools in particular are unable to find the time and resources to battle with the appeals system.
He will also say that exam boards are under no obligation to release their re-grade statistics subject by subject and schools are not told which exam boards are the worst offenders on remarking.
He will point out that figures from exam board regulator Ofqual suggest that 6% of examiners are "inadequate" - translating to a vast number of questions that potentially are inadequately marked.
Mr King, who is HMC chairman for 2015/16, will tell delegates in St Andrews he is calling for a number of changes, including better set and better marked exams to create consistency across subjects and boards and a larger, more skilled and better trained marking workforce. He would also like to see a more fair and transparent appeals process.
"Until this happens, HMC will continue to demand re-marks and intervene with universities who are refusing to honour offers made to mismarked candidates," he will add.
"Independent schools already provide more than our share of qualified examiners and together we need to find ways of encouraging more to take part from all schools and colleges.
"HMC has helped lead the way on reform and under my chairmanship we will not rest until then UK has the quality assured exam system its young people deserve," he will add.
A Department for Education spokesman said: "Parents, teachers and young people need to have confidence that the grades they receive are an accurate reflection of a pupil's performance. That's why we're pleased that the regulator is taking steps to improve the quality of marking.
"Our new GCSEs and A-levels will be gold standard qualifications that match the best in the world. The changes we have made to these qualifications are vital to ensuring that young people leave school prepared to succeed in modern Britain and with knowledge and skills that universities and employers need."