When allegations about misconduct at the school surfaced on Facebook in 2017, Saint Ann’s leaders hired an outside investigator. Emails were sent to the school’s community, requesting that anyone with information step forward.

The investigation, conducted by T&M Protection Resources, a New York-based firm, included interviews with 47 witnesses who reported misconduct from the 1970s through 2017.

“None of the witnesses appeared to be exaggerating or embellishing facts and all seemed genuinely concerned about being as precise as possible when answering the investigators’ questions,” the school said in its letter.

The letter detailed the actions of six male faculty members whose alleged misconduct included having sexual contact with a high school senior and then sexual intercourse after graduation, engaging in sexual contact with a student at an off-campus party, unwanted kissing and inappropriate physical contact. None of the teachers were named, the letter said, because the school found that in some cases the evidence was “not clear and convincing.” All six of the teachers had left the school before the investigation.

“What we tried to make clear in the letter was these were the six instances where the investigator made a judgment that the evidence he was able to compile met the appropriate evidentiary standard,” Mr. Tompkins, who became headmaster of the school in 2010, said in an interview.