Michigan is facing a projected $2.8 billion state budget shortfall. As a result, Governor Granholm has cut $212 million from state public school spending — rousing the ire of parents and education officials around the state. But if Michigan merely converted all its conventional public schools to charters, without altering current funding formulas, it would save $3.5 billion.

Here’s how: the average Michigan charter school spends $2,200 less per pupil than the average district school — counting only the state and local dollars. Put another way, Michigan school districts spend 25 percent more state and local dollars per pupil, on average, than charter schools. Sum up the savings to Michigan taxpayers from a mass district-to-charter exodus and it comes to $3.5 billion.

Anyone who wants to check that calculation can download the Msft Excel 2007 spreadsheet file I used to compute it. It contains both the raw data from the relevant NCES Common Core of Data files, and all the calculations. Among other things, it shows total per pupil spending and the pupil teacher ratio for every charter school and every public school district in the state. (Unlike certain climatologists, some of us researchers not only keep our data around, we’re actually happy to share them).

Journalists who have questions about this file are welcome to get in touch. Note that it is also viewable, I believe, with the free OpenOffice spreadsheet program, though I haven’t tested that.