GCSEs are a "national disgrace", according to a coalition of education experts calling for the exams to be scrapped.
The key figures in the education sector made the comments to Tes after signing an open letter criticising the UK's "mutant exam system".
Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), was among the signatories, who have formed a coalition aiming to fix the "exams merry-go-round" by piloting alternative approaches in schools.
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The open letter, published in The Times, stated that GCSEs are a "good starting point for reform", now that the school leaving age has risen to 18 and "the exam has become less fair".
Among the signatories was Lord Kenneth Baker, who was education secretary when the tests were brought in to replace O-levels and CSEs in 1988.
The coalition, called "Rethinking Assessment", said they believe the current exam system was borne out of "good intentions", but has "mutated into something that neither measures the right things nor is very reliable, and leaves in its wake a trail of stress and unfairness".
They used the letter to argue that "the over-crammed curriculum on which tests are premised ensures 'covering content' matters more than a love for the richness of a subject".
And, "however successful they are at exams", all pupils leave school with only "a partial record of their strengths" – with "no credit" given to those skilled in teamwork, communication, problem solving or creativity, they wrote.
The signatories warned that the system is threatening pupils' mental health, and they are "sick of talk without action".
"The case for change is becoming more compelling by the day," they wrote.
"Many young people find the relentless practice for exams increasingly stressful; depression and self-harm statistics confirm this.
"Thirty or more GCSEs in one month; intense high-stakes written exams couldn't be designed better to induce anxiety."
They also claimed that, "perhaps worst of all", each year an algorithm is used to "ration the number who pass exams".
This means pupils in the UK are granted a qualification only if they are "better than enough of their peers", the group said.
The letter's signatories were as follows:
Peter Hyman, co-director, Big Education; co-founder and first headteacher, School 21
Simon Henderson, headmaster, Eton College
Sarah Fletcher, high mistress, St Paul's Girls' School
Sarah-Jayne Blakemore, professor of psychology and cognitive neuroscience, University of Cambridge
Lord Kenneth Baker, former secretary of state for education
Geoff Barton, general secretary, Association of School and College Leaders (ASCL)
Neil Strowger, CEO, Bohunt Education Trust; headteacher, Bohunt School
Julian Drinkall, chief executive, Academies Enterprise Trust
Robert Lebatto, headmaster, the King Alfred School, London
Tamsin Ford, professor of child and adolescent psychiatry, University of Cambridge
Magnus Bashaarat, headmaster, Bedales School
Alistair McConville, director of learning and innovation, Bedales School
Will Goldsmith, director of teaching and learning, Latymer Upper School, London
Dame Alison Peacock, chief executive, Chartered College of Teaching
Leanne Forde-Nassey, headteacher, The Key Education Centre, Gosport and Havant
Gwyn ap Harri, co founder, XP school, Doncaster
Bill Lucas, professor of learning, University of Winchester
Olly Newton, executive director, Edge Foundation
Sally Dicketts, chief executive, Activate Learning
Meeta Vouk, director, IBM Singapore Research Centre
Rachel Macfarlane, director of education services, Herts for Learning