The government's new qualification for 16-year-olds could limit pupils' choice and fuel inequalities in the education system, campaigners have warned.
The National Children's Bureau (NCB) has raised concerns that the English Baccalaureate Certificates (EBCs) will put many youngsters, including those who have special educational needs (SEN), or are from poorer families, at a disadvantage.
Ministers announced plans for the new EBCs, which will replace GCSEs earlier this year.
Under the proposals the first EBCs, in English, maths and science will be introduced in autumn 2015, with the first exams taken in 2017.
EBCs in history, geography and languages will be introduced at a later date.
GCSEs, or other qualifications, will remain for other subjects such as PE, drama and art.
The government has insisted that the exams system needs to be overhauled, with tougher new qualifications brought
in to help raise standards.
But in their response to the government's consultation on the proposals, the NCB, with the Council for Disabled Children, said they believe that the new qualifications need to be re-thought.
Young people's achievements "should be celebrated in the widest sense", the charity said, with students encouraged to develop a love of learning.
The response says: "The strong focus on academic attainment and a limited set of subjects within the English Baccalaureate will prevent many young people from having the opportunity to show what they are capable of achieving through meaningful assessment."
Playwright and director Sir David Hare called the proposals "insanity".
"At a time when local authorities are strapped for cash and cutting back on inspiring visits to dance, music and theatre events, that the government should meanwhile take away from less privileged children the chance to access these life-changing subjects through a central curriculum.
"The rigidity of the proposed list of subjects means that the arts will now be denied to the very pupils who have least chance of exposure to them in their daily lives. Insanity, and worse – class-reinforcing insanity."
Actress Julie Walters OBE added: "Considering that we have just had the Olympics celebrating our cultural heritage and showcasing bright new talent, it seems ironic that the Government wishes to undermine Creativity and the Arts by side-lining them from the curriculum.
"We should nurture creativity and its power to encourage innovation."
The NCB and CDC add that the proposals could narrow young people's choices in education and future career opportunities - especially for those who are vulnerable or have SEN.
And it says: "Moreover, the restrictive nature of the curriculum, with the focus on six core academic subjects, could lead to a substantial widening of the attainment gap and increase inequality within the school system."
The response says the government's immediate priority should be to "re-establish the credibility for GCSEs, as there will be four more year groups of students taking the qualifications before the first EBC exams are sat."
NCB chief executive Dr Hilary Emery said: "The government needs to seriously reflect upon the consequences of rushing to introduce harder examinations, designed to ensure more students fail.
"Secondary school should be about increasing the opportunities for all young people to have the very best learning experience, which will prepare them to lead fulfilling lives and nurture talent and aspirations.
"Young people have told us that they don't like the narrow, inflexible scope of the new qualification. Their concerns must not be ignored."
The NCB is the latest organisation to voice concerns about the EBC plans.
Sir Nicholas Serota, director of the Tate, said the facts told a "worrying story".
"The arts are a vital part of a rounded education, and that should be available to all. The omission of arts subjects from the English Baccalaureate has already resulted in art teachers losing their jobs, applications for PGCE courses in the arts declining, and children being channelled away from the arts."
Last week the Association of School and College Leaders (ASCL) warned that the qualification may not help schools to improve results for all students
In its submission to the government's consultation - which closes today - ASCL said 96% of its members who had attended recent regional conferences "do not believe that the proposals for EBCs will enable them to raise achievement for all the students in their schools."
The submission adds: "This is a worrying statistic, even if this is an initial reaction which may change as the proposal becomes clearer, since these are the very people who need first to be convinced of the rationale for change.
"They are happy to debate the need for change and the need to raise attainment, but are not immediately convinced that this proposal will have the desired impact."
England's exams regulator, Ofqual, has raised its own concerns with Gove about the reforms.
In a letter to the Education Secretary, chief regulator Glenys Stacey said that the aims for the new qualification might not be "realistically achievable".
She suggested Gove's new English Baccalaureate Certificates might not fulfil every role he hopes they will.
There are "no precedents" to suggest that a single type of qualification can fulfil a number of purposes, she wrote.
A Department for Education spokeswoman said: "The core academic subjects most valued by universities and employers are those that make up the EBacc. These will also be the subjects for the new EBC exams, which will set the benchmark for the whole system.
"Other subjects are of course valuable and pupils will continue to study them - no school will be prevented from offering qualifications in a broad range of subjects."
The government will respond to the consultation in the new year, she added.
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