You need to also understand how funding works. It's paid per pupil but not until the April.
In our borough we had 3 or 4 years of a very low birth rate, but either side were very large birth rate years so you had the scenario of large numbers in years 11 - 8 and then a rapid drop off in year 7, which was manageable.
As the smaller year groups progressed through the school the funding decreased accordingly but we still needed to maintain staffing for the higher birth rate year groups in the upper school, whilst also being aware of the need to plan for higher numbers coming into the school in 4 years time.
We managed as best we could through natural wastage and not replacing staff though we didn't always loose staff in appropriate departments. Obviously running costs stayed the same despite lower pupil numbers and associated lower funding.
Given that the LA was very aware of the situation I do think far more financial support should have been given to schools, acknowledging this blip in pupil numbers and the very real increase in demand for school places that was on the horizon given the higher birth rates coming through plus vast amounts of new houses being built.
These pressures force schools into making unpleasant decisions - replacing experienced (expensive) staff with NQTs (cheaper), cutting number of subjects offered thus restricting choice, cutting school hours reducing PPA cover but passing burden to parents, cutting after school provision, not providing paper, exercise books, getting students to print worksheets at home etc.
Please don't believe the headlines that politicians spout. Education is in crisis and teachers are spending precious time manipulating dwindling budgets when they should be teaching.