I would say 'no' for average earnings. Are you being genuine when you talk about 'average' earners?
The average UK full-time salary was £35,423. For two working full time that's £70,212 gross - £4,368 per month after tax with an allowance of just 5% pension contributions.
Once you start deducting mortgages, bills, etc. I think NOT.
My DH and I take home a little more than this (although I work part-time) - this is a summary of our outgoings. We have a nice quality of life, we aren't extravagant but we do have luxuries because we can afford them.
Mortgage, Council Tax and Life Insurance £1,568
Utilities and TV Licence £176
Home insurance and breakdown cover £38
National trust, Amazon, Netflix,Sky £92
Sofa Repayment £50
Food £750
Cleaner £150
Window cleaner and ironing £70
Kids activities £105
Pocket money £10
Total £3,009
Surplus £1,359
Sounds like a lot. But...
Childcare (3 days CM and wraparound care) £850
Surplus is now £509
Oh yeah, car and fuel £150
Savings (ha!) £150
£209 left over for general living, clothes, going out etc.
We are really fine and comfortable day to day but we have no substantial savings and earn in excess of the average.
We could now afford private school.
And here's the funny bit - I work for an independent school and get a substantial discount. I could afford to send ONE of my sons. And only to prep.
On average salaries it is NOT affordable without special circumstances (no mortgage, significant bursaries etc).
You need to be earning I would say in excess of £100k between you for it to be a consideration.
The caveat is that I live in London so of course that skews things somewhat.