Frederic Lyman’s prep school teaching career spanned just six years, and four schools.

On Wednesday, allegations of inappropriate behavior against him surfaced at Kent Denver, a private day school in Colorado, which means that Mr. Lyman now stands accused of misconduct with students at three of those schools, across three states.

Mr. Lyman was one of 12 men named in an in-depth report on sexual abuse released by Choate Rosemary Hall, the prestigious Connecticut boarding school, in April. Investigators for the school, where he taught in the early 1980s, said that Mr. Lyman had sexual relationships with two students. He stalked one of them, according to the report, and gave her a black eye.

Mr. Lyman was forced out of his job at Choate when administrators learned he had given one of the students herpes. But he left the school with a letter of recommendation, the report said, which allowed him to move on to Kent Denver in 1982, where administrators had no way of knowing what he had done.

In a letter sent to the school community on Wednesday, Kent Denver said that three former students had contacted administrators in recent weeks with complaints about Mr. Lyman.