A lot of schools are going to absorb some of the 20%
And it's all risky, because people don't want to pay £30k for classes with 30 kids in, when they could go to the local outstanding state grammar or whatever.
Let's pick some numbers for the sake of discussion.
Income for a pupil is £20,000 on fees. Reduce this to £16,000. Total school population is 5 X 100. So fee income is £20 million. Just say.pying for 80 members of staff on (AVG £40k), which means staffing costs are around £60k with pensions etc.
If you have 100 pupils in 5 forms each year, and now you have 120, income remaining at £20m.
d need to keep ratios, you need a 5th form, and so extra staff/classes/costs...so you'd have to pay an extra member of staff ££ for being a tutor. You might be able to squeeze those 20 lids across 4 maths sets, but now there's 25 in a class instead of 20. But if you want to keep ratios, staffing costs will have to increase. Or otherwise timetable load increases on existing staffing. As well as increasing administrative burden across the staff.
In addition you have the extra initial spending eg... you need to provide 5 extra chairs per classroom, 20 more textbooks in each subject , , laptops, etc all with the same amount of money. Of it's a boarding school, 20% more.food, 20% more beds, perhaps more staff for ratios, more running costs...
They still have to pay the electricity bills, gas/heating, water etc all increased by extra people... Yet no more money.
The only realistic way to afford it ,is to reduce staffing costs, as that makes up the bulk of where money is spent on workforce.
Also, you can't just magic up 20% extra roll overnight just by reducing fees by 20%, it doesn't work like that.