A Queens high-school principal who already has cost the city more than $500,000 in lawsuit settlements is now being probed for allegedly coercing teachers to give passing grades to failing students.

Department of Education investigators swarmed John Bowne HS in Flushing last week to question staffers about Principal Howard Kwait and the claims of grade fixing, according to sources.

“He puts pressure on the teachers to give passing grades to these kids,” said one staffer. “Some of these students they are pushing through are not ­college-ready.”

Officials confirmed that DOE’s Office of Special Investigation is looking into the accusations.

“Academic integrity at all our schools is critical, and we investigate any allegation of academic improprieties,” said DOE spokeswoman Devora Kaye.

Kwait could not be reached for comment via phone or e-mail Wednesday.