In 2018-19 the council will spend £176 less on each pupil than in 2014-15, after the figures are adjusted for inflation.
Teachers say that schools across the country are “on their knees”, warning that funding cuts are causing “untold damage” to children and young people’s education.
In 2014-15, spending per pupil in Northamptonshire was the equivalent of £4,352, in real terms.
This financial year, that figure is £4,176 - a 4% drop over four years.
In England, per-pupil spending has fallen by 2.8% in real terms over the four years, from £4,657 in 2014-15 to £4,528 this year.
Since last year, the spend per pupil has fallen by £28.
The annual schools’ budget details how much each council plans to spend on education over the financial year.
The money comes directly from the Government in the form of a centralised grant - in Northamptonshire, the allocated budget for 2018-19 is £516.6 million.
The spending per pupil figure covers all the costs of education - from teacher salaries to textbooks.
The Department for Education said that school funding in England will rise to a record £43.5 billion by 2020, and that funding for pupils with additional needs has risen from £5 billion in 2013 to over £6 billion this year.
“We know we are asking schools to do more,” said a DfE spokesperson. “That’s why the Education Secretary has set out his determination to work with the sector to reduce cost pressures, including things like stationery, energy and water bills.”
The spokesperson said: “There is more money going into schools than ever before.”
The National Education Union said that the DfE’s claim is “disingenuous”, “misleading to parents” and “insulting to schools”.
NEU’s joint general secretary Dr Mary Bousted said: “It ignores the impact of inflation and the increase in student numbers.”
“Schools are on their knees,” she said. “They need significant investment to reverse the cuts of the last three years, address historic underfunding of some areas and tackle the crisis in school funding for pupils with special needs.”
The National Education Union said that funding cuts have led to subjects like dance and drama being cut from the curriculum, and that many schools are also cutting back on after-school clubs and stopping school trips.
Dr Bousted said: “This has a massive impact on the educational and life experiences of children, particularly for those from families on low incomes.
“Schools lack essential resources, and it is now common for head teachers to send out letters pleading with parents to donate money to plug the gaps.”
According to the NEU, cuts in funding per pupil lead to schools increasing their class sizes, in order to meet costs.
The NEU said that bigger classes mean pupils get less time with their teachers, and that teachers have more work to do.
The National Association of Head Teachers said they were concerned that schools could no longer afford to employ specialist staff for children with special education needs.
“It’s becoming harder for mainstream schools to be inclusive,” said NAHT head of policy Valentine Mulholland.
She said: “Funding cuts are not just affecting the education of children, they’re affecting the wellbeing of children.
“We need to be able to support all students, not just the most able ones. The most vulnerable pupils are being left behind.”
The Local Government Association said that it shares the concerns of schools over the “squeeze” on funding, and the possible impact on the quality of education children receive.
LGA’s children and young people chairperson Councillor Antoinette Bramble said: “To make sure every school is adequately funded, the Government should introduce three-year budgets and allow councils to work with schools to set budgets that reflect local need.”