City Hall’s reluctance to give charter schools space in public buildings is costing taxpayers tens of millions of dollars in needless rental costs, a new report shows.

Now we know: Mayor de Blasio is sticking by his policy on charter schools — “separate and unequal.”

That’s the thrust of the city’s offer of 1.000 middle-school seats to Success Academy, which needs 1.700 to accommodate all its kids.

Brooklyn chess teacher Boris Izrayelit, 33, had to keep his eyes on two games at once at the World Chess Championship on Friday.

World champion Magnus Carlsen of Norway and challenger Sergey Karjakin of Russia were playing the sixth game of the match in the Fulton Market Building in lower Manhattan. In an adjoining room, Izrayelit watched them on video screens while next to him, two of his students, Nura, 10, and Vincenzo, 9, were playing a game of their own.

Dear Mayor de Blasio,

The city’s proposal to temporarily house Success Academy middle school students from five Brooklyn elementary schools in just two locations is not “reasonable, adequate, or comparable.” In fact, the proposal is an aggressive affront to families, many of whom had believed the Department of Education last year when it promised to find a permanent site for their children’s middle school.

Each year, the Department of Education is required to publish a Blue Book that serves as the city’s official record of how many seats are available in local district school buildings. This year’s Blue Book reveals that the districts where charters are pursuing co-location — in which they would share space with district public schools — are vastly underutilized, with enough open space to accommodate 94 charter schools.

The city has been fudging its school-vacancy numbers to prevent charters from expanding, critics charge — citing a report quietly released by Mayor de Blasio’s own education honchos.

Kids come as they are. Good schools find their curiosity and build their hope.

The topline job of schools is to renew a student’s sense of possibility and give her what she needs to make it real.

I think of schools that do this as the real renewal schools — to borrow a phrase.

Hundreds of city children are at risk of being “educationally homeless” next fall — victims of Mayor de Blasio’s refusal to give charter schools room to grow.

Research backs up what common sense dictates: Students in good schools learn more in a year than those in poor schools.

For instance, Stanford University has found that students attending New York City charters learn the equivalent of five more months of math in a year than their peers in traditional schools. Comparing good traditional schools against low performers also reveals large gaps in learning.