According to the school’s records, Mr. Cobbett was forced to step down as the girl’s adviser and coach, but at least initially, the administration decided to allow him to “retire quietly at the end of the year.” However, after administrators spoke with the girl’s parents, who were concerned that the teacher’s abrupt departure might reflect poorly on their daughter, he was allowed to remain at Choate for another 10 years.

The investigator also looked into the case of Frederic Lyman, an English teacher and house adviser, who, the report maintains, would often serve his students tea spiked with rum, and who was accused twice by young women in his classes of having sex with them and infecting them with herpes. When administrators learned of this in 1982, Mr. Lyman was permitted to retire at the end of the school year. Before he left, Mr. Lyman wrote a letter to the administration, saying that in his remaining days at Choate, he promised “not to be the source of any new rumors or incidents.”

Charles Twichell, then the dean of faculty, wrote Mr. Lyman a letter of recommendation referring, in what the report suggests was perhaps a hint at Mr. Lyman’s behavior, to his “easy familiarity with students.” The letter continued: “In this area, the ‘social’ one, he shows reluctance to accept conventions often characteristic of those in college during the late sixties.”

Mr. Lyman, who declined to speak to the investigator, got a job at another private school.

Choate administrators often showed remarkable patience toward popular or longtime teachers accused of misconduct. Charles Timlin, for instance, taught English and Latin at the school from 1981 to 2010. In his final year, the report said, a female student accused him of kissing her several times and saying that he wanted to have sex with her. When the headmaster, Edward Shanahan, found out about the incident, rather than firing Mr. Timlin, he had the teacher agree to various conditions under which he could stay at Choate.

Mr. Timlin had to move out of the girls’ dormitory where he was an adviser, and had to meet with a psychiatrist. He also had to sign a resignation letter that might become effective at any moment.

But the student who accused Mr. Timlin was furious about these terms, as was her father, who is said to have “expressed his anger and his feeling that the school had not acted fairly.” Eventually, Mr. Shanahan fired Mr. Timlin and reported him to the Connecticut Department of Children and Families. The agency later wrote its own report, noting that Choate had waited more than two months before alerting the student’s parents. The school “did not report the alleged abuse” to state officials “within the 12 hours they are required to do by law,” the agency said.

Mr. Shanahan, who did not respond to phone calls seeking comment, now runs a high-priced private school in Beijing and is a life trustee of Choate.