A former Queens biology teacher who allegedly forced an underage student to repeatedly have sex and demanded she have two abortions skirted authorities after a prominent Catholic school quietly fired him, allowing him to work for years in city public schools, officials report.

Rodney Alejandro abused the 15-year-old girl at St. Francis Preparatory School in Queens, and then went on to work for the Department of Education, a 2015 probe by the city’s Special Commissioner of Investigation charges.

First a city substitute in 1998-99, he worked from 2004 to 2010 at Robert Wagner Jr. Secondary School for Arts and Technology in Long Island City and was fired after his state license expired, officials said. He then went on to teach at a religious school in Georgia.

His reported victim, now 43 and living in Queens, declined to comment but confirmed to The Post horrendous details she published in a 2014 blog. The Post is withholding her name.

Alejandro, now 52, allegedly began raping the girl in January 1988.

By the summer of 1988, she got pregnant for the first time and she says “Alejandro forced her to have an abortion,” the SCI reports.

When she got pregnant again in January 1989, “Alejandro insisted upon an abortion,” the report says. The student says she became so depressed that she failed the school year.

“At this point, I was suicidal,” she wrote.

St. Francis Prep never disciplined Alejandro. Instead he “resigned and left the school in good standing,” the SCI found.

St. Francis Prep did not return calls for comment.

The school, whose alumni include crusading former cop Frank Serpico and former Yankees manager Joe Torre, had been the target of a $17 million lawsuit charging sexual and physical abuse by teachers at the school in 2013. The federal suit was dismissed in 2014.

In that same year, Alejandro’s alleged victim decided to tell her story to SCI investigators and also met with a rep from the Queens District Attorney’s Office who told her that the statute of limitations had run out and “a case against Alejandro would not be pursued,” SCI said.

Alejandro went on to teach at Mount Pisgah Christian School in Alpharetta, Ga., in September 2011, but by December 2012 the school asked him to resign because he didn’t disclose a prior termination.

Alejandro is ineligible to work in DOE schools again. He could not be reached for comment.