A retired teacher from Bristol indecently assaulted boys at two Catholic boarding schools in the 1970s and 80s, a court heard.
David Lowe, 61, is said to have targeted 10 pupils aged from eight to 13 between 1978 and 1984.
The offences are alleged to have taken place at Westminster Cathedral Choir School and Ampleforth College in North Yorkshire.
Lowe denies 15 counts of indecent assault of a boy aged under 14.
A jury at Southwark Crown Court heard Lowe invited the youngsters to his flat and "spanked" them when they had broken school rules, and touched them intimately under their bedding when he carried out dormitory checks.
He is also alleged to have molested other pupils by telling them that he wanted to "massage" them.
In 1981, when Lowe was working at Westminster Cathedral Choir School, one of his alleged victims complained about being repeatedly abused by him and the teacher left the school soon afterwards.
A short time later, Lowe began working at Ampleforth College, which is run by Benedictine monks, where he allegedly assaulted four of his 10 victims.
The court heard that one of Lowe's alleged victims was only prompted to come forward after he received an email from the former teacher last year, after he had already been charged with a number of indecent assaults.
The man told police: "There was only one reason why this man would get in touch with me. It's not because he wanted to meet up and have a coffee and chat about life. It was because something had happened to him.
"He was the man that had abused not only me, but a number of pupils at the choir school."
The man described Lowe as a "popular" in school and said how it was strange that other staff who were "so vigilant" did not notice what was going on.
The trial continues.