A secondary school will cut an hour of teaching a week from the autumn in a bid to save £100,000.
Joe Wincott of The Sandon School in Chelmsford, Essex said an extra £1.3bn promised by the government was too late to help it in the next academic year.
The head teacher said cutting lessons from 26 to 25 hours a week would allow him to balance the school budget.
Education Secretary Justine Greening said per pupil funding was set to go up from £4,100 to £4,800 in 2018.
Mr Wincott said the school budget had been cut by £450,000 since 2011 and he had reduced the costs of “everything from power supplies, examination and photocopying”.
He said: “We were down to the situation where we were unable to balance our budget for 2017-2018, so we took the decision… to drop to 25 hours, which is what most schools deliver.”
Parents at the mixed comprehensive school, which has 1,270 pupils aged 11 to 18 and was rated good in its last Ofsted inspection, had been “remarkably understanding”.
But the head teacher added a “significant number of pupils” were entering the school system, and pay, pension and National Insurance contributions were all due to increase.
As a result, he believes the promised extra pupil funding in 2018 will “probably put us where we are now, but without having to make cuts to staff”.