Data provided by campaign group Stop School Cuts, which is run by the National Education Union, shows that 81 of the 87 schools across the borough will face cuts totalling £3.3m.
It equates to a cut of £102 per child.
Penistone Grammar Advanced Learning Centre will need to find more than £363,000 to recuperate the cuts it is expected to face next year.
Coun Hannah Kitching, who represents Penistone West and is the leader of the Liberal Democrats in Barnsley, has called on Labour in the town to fight for better funding for its schools.
She told the Chronicle: “Under this government, schools must choose between teaching children or heating classrooms.
“Headteachers are warning that they will have to cut teaching assistants, mental health support and school clubs in order to make ends meet.
“Penistone Grammar School has long been the worst-funded school in Barnsley borough, and one of the worst-funded state maintained secondary schools in the whole country.
“It is disgraceful that it is now facing further cuts.
“We need to see Barnsley Labour fighting for better funding for all our schools, but especially for Penistone Grammar School which is hardest hit.
“Liberal Democrats know that it is crucial to invest in our children’s futures.
“Parents and teachers will be rightly angry if the Chancellor announces more cuts to schools and colleges next week.
“The Conservatives are planning more public spending cuts to pay for their own economic incompetence.
“School trips are already being axed, teaching assistants are being laid off and urgent classroom repairs are being ignored.
“Rishi Sunak and Jeremy Hunt must confirm urgently that they will not cut real-terms funding for schools and colleges during next week’s Autumn Statement.
“The Conservatives must not balance the books on the backs of our children and young people.”
Whilst across the border in MP Dan Jarvis’ Barnsley Central, Carlton Primary School, Mapplewell Primary School and Meadstead Primary School are amongst the worst-impacted with cuts of up to £306 per child.
Dan said: “The data is very worrying, and I am deeply concerned about the impact cuts would have on educational outcomes in Barnsley.
“These cuts will be detrimental to learning, with larger class sizes, reduced curriculum options, and reduced individual support for pupils.
“It will also mean unmanageable workloads and further real-term cuts to hard-working teachers’ pay.
“Schools are straining every possible sinew to try make efficiency savings, but they cannot continue to weather this storm.
“We must ensure our teachers and staff - who do so much for pupils - get the resources and respect they need to give our kids the best start in life.
“The Prime Minister promised to restore per-pupil funding to 2010 levels at his Spending Review last year, it’s vital he keeps this promise, stops the underfunding of education and invests in this generations’ futures.”
Stop School Cuts has started a petition which has already been signed by more than 5,700 people.
A spokesperson said: “Next year, a staggering 18,060 schools face year-on-year funding cuts totalling £1bn in real-terms.
“For millions of children, these cuts will lead to larger class sizes, fewer subject choices and reduced individual support for children.
“For teachers, it means more real-terms pay cuts, more unmanageable workloads and less time to teach each child.”
Secondary schools are set to be much worse-off than they were previously as the five institutes - Horizon, Barnsley and Darton Academy, Outwood Carlton and Penistone - will see cuts of around £800,000.