New York City Mayor Bill de Blasio has long regarded charter schools with antipathy, particularly the practice of allowing them to take advantage of unused space in district buildings in a city where real estate prices are through the roof. He shares this opposition to “co-location” with Randi Weingarten and UFT. The union even pressed a (losing) suit against the state Department of Education over the issue.

But here’s a fact that doesn’t seem to surface during discourse about the pros and cons of charter schools and traditional schools sharing space: 63% of New York City schools collaborate on space and only a small percentage of these involve charter schools.

According to a 2014 report from Marcus Winters,  “1,150 (63 percent) of the city’s  1,818 public schools are colocated. Of these 1,150 colocated schools, 115 are charter schools.

De Blasio’s bone of contention with co-location isn’t about sharing space. It’s about charter schools themselves. When first elected almost three years ago, he tried to completely shut down charter school expansion in a city with a 50,000 student waiting list. Parent outrage — plus a bill pushed through by Gov. Cuomo that forces the city to subsidize rent for charters that have to pay for facilities —  has barely muted his anti-choice impulse

But the price gets paid every day by children who lack access to quality public schools, charter and traditional, and in taxpayer dollars. According to the NY Post, “the city’s already shelling out $40 million a year for charters’ rent, and that amount is likely to soar if de Blasio keeps needlessly refusing to let good schools open up in space that’s going unused.”

But does co-location impose burdens on traditional schools? Here’s Winters:

I find no evidence that colocations, whether with charter schools or with traditional public schools, in New York City have any discernible impact (positive or negative) on student achievement in a traditional public school. This result is consistent across various measures for the existence and magnitude of colocation.

StudentsFirstNY ties Mayor de Blasio’s animus towards charters to his reliance on the support of UFT:

[Charter schools are an] existential threat to the perceived best interests of the United Federation of Teachers, which involve the jobs, pay and perks of its members – and never mind the kids. Now the union is calling the public-education shots, and it has decreed that the charter baby be drowned in the bathtub – and, again, never mind the kids.

Meanwhile, scarce space for schools is underused, about 150,000 seats available in 67 school buildings.

Here’s another little-known fact:  UFT’s own charter school was — wait for it — co-located in  J.H.S. 292 .  (The school has since closed down due to “organizational dysfunction, fiscal distress,”  and lack of student growth.)

Last summer the de Blasio administration denied co-locations to 45 charter schools. The state education commissioner ruled that the Mayor violated state law in 44 of those cases and the charters all won space during the appeals process.  Bronx State Senator Ruben Diaz, who is regularly mentioned as a possible contender for mayor, said at the time,  “This was a charade, Charter schools have proven to be good for black and Hispanic children. Why wouldn’t you want them?”

That’s a question that 50,000 children are asking too.