GOP state Sen. John Flanagan should knock off his petty obstructionism.

Flexing his executive muscle at the right moment on the right issue, Gov. Cuomo is calling back the Assembly and Senate for an extraordinary session days before mayoral control of the city schools is set to expire, to extend the critical authority for a year. No horse-trading. No shenanigans. And no excuses left for Sen. John Flanagan, who leads the Republican-controlled Senate.

For years, Flanagan and fellow Republicans were just fine, thank you, giving New York City’s top elected official the power to run the nation’s largest education system.

They understood it would be unconscionable to return to the chronic dysfunction that marked the old, unelected Board of Education. And to go back to the corrupt fiefdoms that were the 32 community school boards, chosen by 3% voter turnout.

For years, Flanagan and fellow Republicans acknowledged that holding an elected chief executive responsible for the schools delivered accountability, and therefore results.

Like graduation rates now at record highs. City kids’ scores on state math and English tests on the rise. Attendance up. Violence down.

Plenty of work to be done, but a system overall, even under a union-friendly mayor, a bit less dominated by the teachers’ union’s agenda of inertia.

For years, Flanagan and fellow Republicans knew to leave well enough alone. Oh, but that was when the mayor was named Mike Bloomberg — who, by the way, in case you forgot, was the largest single contributor to Republican campaign coffers.

With Bill de Blasio in charge, Flanagan suddenly has grown philosophical objections. Kind of.

He offered to extend control, but only if the Democratic-controlled Assembly would raise the cap on charter schools and vote in tax credits for private and parochial schools.

Even those who support tax credits and want more charters, as we do, could see through the cynical stunts. Through the clunky tries at dealmaking, Flanagan admits that he’s just fine with mayoral control. He just wouldn’t agree to pass it without getting a pound of flesh in return.

Now comes the reckoning: Members have to return to the Capitol to consider a simple gubernatorial bill to keep mayoral control on the books. The mere year extension is too stingy, but it makes it all that much harder for the Republicans to say no.

If Flanagan wants to go right back home, all he has to do is drop his petty resistance, say yes to the bill and live to fight another day. If he is so bent on making life hell for de Blasio — and, by extension, the kids of New York City — he’ll sit on his hands.

Simple choice, really.