They are not imho.
Aside from Religious schools and a few High end Prep Schools and occasional Home schooling the concept of privatizing education has been much talked about with little actual on the ground movement for many years.
Even with a voucher system (which I dont like) I doubt there would be many who participate.
If it did ever catch on in a meaningful way one would think the local taxation on Ed would likely diminish with less schools and staff being necessary--I doubt it will ever happen though.
Frankly over the past 20 years or so the opposite has occurred. The city I was in had many religious schools and most have closed with the kids (primarily K-6) being absorbed into the public system. There were well over a thousand kids requiring building additions and teaching staff increases thus increasing the BOE budget.
The ripple effect shortly had impact on the middle and high schools as well.