I am an atheist.
I think YABU.
I wouldnt hate you for doing what you propose, as I know your motives are good. (You just want the best for your child.)
But I do think it's wrong to lie. It sets a very bad example to your child .... that lying/bending the truth is the correct way to live your life and get what you want/need.
So, (to me), 'faking' religion, (or even just faking an interest in it), shows a lack of personal integrity and is perhaps quite immoral. Is that the sort of education you want for your child? (Education starts at home don't forget.)
Of course, if I were facing the threat of death, (or something else quite horrible), I, (& almost everyone?), would happily renounce our current beliefs, (and/or lack of faith), and swear on the ".......", (name any kind of religious book here), that we were true believers of " ...", if doing so would save our skins. (And sod the morality of lying in such circumstances!)
But is this issue, (ie schooling), SUCH a big deal you are willing to sell out your existing honesty & integrity? (I thnk it's quite hard to get those qualities back once you have let them go?)
Therefore, I'm with your DP. (Play the game with a straight bat! At least for now?)
I would agree with you that a private school might be a better choice if you can afford it, (a big IF), and if the local, (non faith), school options are as bad as you imagine.
I also agree with the poster who said it's a rotten system. Why should people of faith, (some of whom are not very sincere about their beliefs), get a better education than some, (more truthful/moral), atheists?
And why oh why can't there be loads of outstanding schools for kids of atheists? (Is it just a question of insufficient funding?)
The system sucks for you. (And I think faith schools shouldn't exist.) But, personally, I don't think I could bring myself to "fake religion" just to get my kid into a better school.
I'd look at all the alternatives, and also try to complain re the system, so maybe future atheists will not have to think about lying to get a fairer choice of education.
Best of luck.