Thousands of fired-up charter school supporters descended on City Hall Wednesday demanding that Mayor de Blasio put an end to education inequality by expanding the number of charters.

Bronx Borough President Ruben Diaz Jr., a potential mayoral candidate in 2017, promised the crowd he would “always be a supporter of charter schools” and echoed demands that the mayor give parents more options for their kids.

“Mr. Mayor, what we’re saying here today is this: The public-schools system is your system. Charter schools are a part of that system, and all we want from you, Mr. Mayor, is to treat them equitably,” Diaz told the crowd, which marched en masse in a sea of red T-shirts over the Brooklyn Bridge from an earlier rally in Cadman Plaza.

Organizers estimated the size of the crowd at 18,500.

One parent after another took the microphone to tell how charters had saved their kids from failing neighborhood schools.

Natasha Shannon, 37, of Washington Heights, a stay-at-home mom whose girls all go to Success Academy schools, said the mayor would never send his own children to a failing public school.

Brooklyn parent Patrick Cabiness lambasted PS 67 in Fort Greene, where his 8-year-old son Jaylen is a third-grader.

“I have seen firsthand how the mayor is failing our public schools. At my son’s school, nine out of 10 kids do not read on grade level,” he fumed at the microphone.

“The mayor has promised by the year 2026, all second-graders will read on grade level. By the year 2026 my son will be 19 — he needs a good education now !”

Tracia Gill of Flatbush said her kids brave brutal commutes each day just to attend highly rated schools.

Her son, Otage Miller, is a senior at the High School of Math, Science and Engineering at City College in Harlem, a specialized school, while her daughter, Jadah Gill, 12, is a seventh-grader at Achievement First Endeavor in Clinton Hill, a charter.

“My daughter gets up at 5:30 in the morning and takes three trains to get to school. My son has to go from Church Avenue to the last stop on the B train, and that’s an hour and a half each way. They should not have to get up at that time in the morning and travel that far to get to a great school,” she said.

The huge rally featured thousands of teachers, parents and kids, whose bright-red T-shirts read, “I Fight to End Inequality” — a pointed reference to the mayor’s own pledge to battle economic inequality.

Speaking on WINS radio Wednesday morning as the rally was getting under way, de Blasio said he’s focused on serving the larger school population.

“Our vision for the New York City public schools is that every school is going to be brought up to the point of excellence. And look, the vast majority of our kids — about 93, 94 percent of our kids — are in traditional public schools. We have to turn them around,” he said.

The rally was sponsored by Families for Excellent Schools.

Additional reporting by Carl Campanile