Schools in England are being promised an extra £1.3bn per year in their budgets, alongside a shake-up of how funding is allocated.
But the cash for schools will be taken from elsewhere in the education budget, such as building free schools.
Education Secretary Justine Greening said she recognised there had been public concern over school funding during the general election.
But Labour’s Angela Rayner said there “wasn’t a penny of new money”.
“They are not committing any new money and have not been clear about exactly what programmes they will be cutting to plug the funding back hole,” said Ms Rayner.
Ms Greening told the House of Commons said that this “significant investment” would help to “raise standards, promote social mobility and to give every child the best possible education”.
The government has announced more frontline cash for schools – with £280m being cut from the free schools budget and £315m from “healthy pupils” projects.
The Institute for Fiscal studies says the extra money is more generous than promised in the Conservative manifesto – but will still mean that schools will on average face a slight real-terms budget cut of 0.4%.
“The government finally appears to be listening,” said Jules White, a West Sussex head teacher who co-ordinated a campaign over funding shortages.
But he cautioned that any increase would need to keep up with “rising pupil numbers and inflationary costs”.
Geoff Barton, leader of the ASCL head teachers’ union, said this was a “step in the right direction and an acknowledgment of the huge level of concern around the country on this issue”.
But he said schools would still have to see the implications of the money being “saved from elsewhere in education budget”.
Chris Keates leader of the NASUWT teachers’ union called Ms Greening’s statement “a recycled announcement of recycled money”.
Jo Yurky, who headed a parents’ campaign over funding, said this was “positive news” and an “amazing turn-around” in attitude from ministers, but pressure needed to be kept up on protecting funding.
School funding became a major issue during the general election, with school leaders and teachers’ unions warning that budget shortages would mean cuts to staffing and subjects.
They pointed to evidence from the National Audit Office and the Institute for Fiscal Studies, which warned of £3bn funding gap and schools facing an 8% real-terms budget cut.
During the election, the Conservatives had promised an extra £1bn per year, which on top of planned increases, would have meant the core schools budget rising by about £4bn in 2021-22.
Most of this extra funding was going to come from scrapping free meals for all infants, a policy which was subsequently ditched.
Under the plans announced by Ms Greening on Monday, the overall core schools budget will rise by £2.6bn between 2017-18 and 2019-20.
All schools will receive at least an increase of 0.5% in cash terms.
The Liberal Democrat education spokeswoman Layla Moran said: “This is a desperate attempt to pull the wool over people’s eyes.
“Schools are still facing cuts to their budgets once inflation and increasing class sizes are taken into account.”
As well as concerns about the overall amount of money available, there has been controversy over how it is divided between individual schools.
Ms Greening said the new formula would go ahead and would address unfair and inconsistent levels of funding.
Under the new arrangements, from 2018-19, the minimum funding per secondary pupil would be set at £4,800 per year.
For many years there have been complaints that schools in different parts of the country were receiving different levels of per pupil funding.
Details of an updated version of the formula, with budgets for individual schools, are being promised for the autumn.