If you want more of a comparison of how wasteful (non efficient) and ineffective public schools are - just compare them to equivalent private schools. They turn out better test scores and spend around 25% that of public schools per student.
Which ones do you consider "equivalent"? Private schools that are the default choice of school for their area and aren't allowed to be selective about what students they admit/retain?
I don't believe you. Proof?
I certainly hope that any parent would have earned far more than $10k working the same hours they spent teaching.
To be valid you'd really need to do a total accounting of time and costs. The means lost income by the parent offset by time not lost due to driving to/from school and such.
Ignorance is bliss, just like unsettlingly blissful homeschoolers.
When you see this kind of statistics you immediately ask yourself who wants what from you and why. Of course the school district is more expensive, they have to maintain their buildings, transportation, and have to offer up remedial services by law. Most of all, they have to pay the teachers' wages, and the opportunity cost for the parent not taking work outside the home isn't counted.