i don't think that public schools are particularly efficient at using money. They spend money on stupid things that have nothing to do with education (i.e., middle school football teams), they suffer from administrative bloat due to decades of unfunded mandates and a litigious society, and most of them have to keep up with legacy facilities that are inefficient and costly to maintain, just to name a few factors.
What I take issue with is the notion that the solution to these problems is to just say "fuck it" and set up a whole new parallel education system. Time after time, that new system can only be accessed by the comparatively wealthy kids/kids with the most competent parents, and the poorest kids with the crappiest parents get left in the legacy system. That's not an efficient use of resources, system-wide, either. Not to mention the parallel notion of just slashing education funding across the board, without any concomitant reduction in unfunded mandates or administrative structures, and just telling the schools to educate more kids with less money.
That's not reform, that's just giving up on a bunch of our kids.
By the way, the Washington, DC data notwithstanding, there is a large gap in per-pupil expenditures between poor districts and rich districts in this country. (PS, NC and most of the south actually do pretty well on this, which is great). When you dig into the data, you will find that middle-upper class US public school students in these rich districts actually beat almost every other country in those global standardized tests. It's the poor districts that drag our global scores down.
http://hechingerreport.org/the-gap-between-rich-and-poor-schools-grew-44-percent-over-a-decade/ https://www.washingtonpost.com/news/local/wp/2015/03/12/in-23-states-richer-school-districts-get-more-local-funding-than-poorer-districts/