I've self-organised something a bit like this myself without a "specialist" financial product for it (and with a relative kindly saying they will help when the time comes) but it seems odd that there isn't anyone in the financial sector trying to capture a long term savings customer with a product like this.
School fees are obviously expensive and obviously out of reach for a lot of people, but they could be closer to being affordable for more people with the right planning.
Say you have a child currently in Y1 of a state primary school. You are happy enough with the state options at primary level but are concerned about the local state options at senior level and would like to be able to consider going private.
The local school fees are typically around £16,000 per year. With your current income and diverting all you can to this, the best you can manage to have spare is circa £6,500 per year - nowhere near enough.
But starting senior school is still 6 years away - so you put that £6,500 into savings, increasing the amount each year to keep pace with inflation. When y7 comes around maybe you don't need to go for private school after all, in which case you have just released a massive windfall of cash to do something else with. Or maybe you do now have fees to pay (which will also have risen with inflation) - so you keep paying in the amount you can but 3 times a year you are taking out a chunk more than you put in, so the balance gradually reduces.
By the start of the 4th year of senior school the balance of the savings account hits zero, and you now need a loan. But by this point you have a 10 year history of regular reliable savings built up, and this is the advantage of a dedicated financial product for this. At the point where the balance hits zero the account converts to a loan account. You continue paying in what you can each month but taking out more than you put in 3 times a year when school fees are due. By the end of A-levels you are significantly in the red - but then school fees are over. You keep paying in for the next 4-5 years and eventually you have paid off the debt.
If something like this existed (and if you aren't passionately against private education - in which case please express that opinion on other threads, thank you) would you use it?
I calculated the maths for how it would work and generated the attached graph.