On average, it costs $10,615 to send a kid to public school for a year. (That's federal, state and local government spending combined.)
As the map above shows, that one number masks a huge variation. Utah spends just over $6,000 per student; New York and the District of Columbia over $18,000.
There's even more variation when you get to the district level. Detailed figures and lots more data (including district-level spending) are available in a report the Census Bureau released today.