Nearly all 134 of Sheffield's primary school will be negatively impacted by changes to funding, it has been claimed.
A Sheffield headteacher said 128 out of the city's 134 primary school will be 'negatively impacted' by the Government's new national funding formula when its fully implemented in 2020.
It comes after the Star launched a campaign calling for fairer funding after it emerged that Sheffield schools are the worst funded out of all the major cities in England.
The Department of Education said that 'no school in Sheffield will lose funding' and schools will attract an increase in funding of 6.6 per cent - equivalent to £20.4 million - when the formula is implemented in full.
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But education officials said this increase is not in line with inflation and rising costs and although most secondary schools will see their budgets increased, nearly all primaries will see them cut.
One city headteacher said she will lose more than £500 per pupil, totaling over £75,000 in 2020.
If her children were taught in Nottingham - where pupils get £589 more per pupil than Sheffield - her school would receive £160,143 more every year, she said.
"My school will not be viable long term," she warned.
She said that the number of support staff, after school clubs and pupil support programmes will all suffer, resources will be at a 'bare minimum' and staff training opportunities will be 'non existent'.
She added: "We are currently a high achieving school with excellent outcomes.
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"I have no doubt that attainment and progress will be affected as well as the availability of staff to support the emotional and well being needs of pupils.
"We will have to do even more with even less.
"The Government has asked schools to make cuts and to work together to find a way of reducing costs. I have already done this.
"Schools have had additional costs applied over the past few years.
"We have nowhere else to cut back apart from front line staff - teachers/teaching assistants which will impact heavily on the quality of education we provide.
"This is a dire situation facing education across Sheffield and in other areas nationally."
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Another headteacher said she would have no alternative than to increase class sizes and cut staff.
"We are a small school and budget changes of this magnitude mean only one thing – staffing cuts," she said.
"This means that in my school, which has recently been praised by Ofsted for the quality of education, care and support which we provide, key members of staff will be lost.
"There will be no alternative but to create much larger classes and many of the additional services which we provide to support our children’s mental health and wellbeing will be lost.
"We will have to consider the levels of experience of any new staff who we appoint and more skilled and experienced teachers will be out of our reach.
"This is no way to improve educational standards. It cannot be right that other cities are receiving much greater levels of funding than Sheffield.
"Why our children deserve less than others I simply cannot comprehend."