My favorite response to the voucher debate is that most politicians who are against vouchers... send their children to private schools! (In D.C. at least, where public schools perform very poorly.)
The main point of the debate is not whether some private schools are able to educate better than public schools. It is whether subsidizing private schools will raise the overall quality of education.
DC spent about $20k/year per student in 2014. That's among the highest spending level in the nation [3]. I believe that figure is closer to $25k/year in 2016. About a third of the states spend less than half per student than DC [4].
[1] http://www.sidwell.edu/admissions/tuition-and-fees/index.asp... [2] https://www.labschool.org/page/admissions/tuition-and-fees [3] https://www.washingtonpost.com/news/local/wp/2015/06/02/the-... [4]http://www.governing.com/gov-data/education-data/state-educa...