An elite Brooklyn prep school has been slapped with sanctions for destroying evidence of an internal investigation into allegations that a former football coach molested dozens of boys before being forced into retirement.

In addition, lawyers for nine men suing Poly Prep Country Day School over their alleged abuse can contact five other former students who reported being victimized by the late Philip Foglietta of abusing them during his 25-year tenure.

Brooklyn federal Magistrate Judge Cheryl Pollak said Poly Prep and its lawyers were “clearly on notice” to keep records related to its 2002 probe due to “the potential for litigation” over Foglietta’s alleged perversions.

A lawyer hired to investigate what the school termed “credible allegations” against Foglietta — who died in 1998 — said he tossed his notes sometime between November 2006 and February 2010 as part of routine housekeeping, according to Pollak’s ruling.

But Poly Prep and its lawyers failed to ask Peter Sheridan for a copy until six months after the school was slapped with a civil-racketeering suit in 2009 — even though it had already been sued over Foglietta’s alleged abuse.

“In light of the fact that two of the four potential times that Mr. Sheridan lists for when he might have discarded his notes are October of 2009 and February of 2010, it is possible that, had counsel contacted Mr. Sheridan shortly after this case was filed, they might have obtained the notes prior to their destruction,” Pollak wrote.

As punishment, she ordered the Dyker Heights school to pay the plaintiffs’ legal fees connected with their efforts to track down the “obviously relevant piece of evidence.”

Pollak also said the plaintiffs’ lawyers can reach out to five of six other former students to determine “when, how, and to whom” they told the school that they had been abused by Foglietta.

Pollack cited “the facts and new witnesses that have been discovered since May 2010,” when she ordered Poly Prep to cough up its “investigative records” regarding Folglietta, as well as his personnel file and records.

The sixth ex-student, she noted, has asked Poly Prep “not to disclose his name.”

A spokeswoman for the school’s law firm said: “We are currently reviewing the judge’s order with our client and will determine the best course of action following that review.”

“Our client, Poly Prep, puts the safety and well-being of its students above all else,” spokeswoman Marjory Appel said.

“In light of the facts that we described to the court, we believe our firm acted properly in connection with the handling of discovery in this matter.”