Head teachers say they face "difficult choices" over what their schools can afford, as a new report says they could be forced into further cuts next year.
The Institute for Fiscal Studies (IFS) says costs will outpace funding for schools in 2025-26.
Schools say that means they will struggle to fund the government's proposed pay rise for teachers, as well as the support needed for children with special educational needs.
The Department for Education (DfE) said it would work with schools and local authorities to provide a "fair funding system that directs public money to where it is needed".
