Dennis Young denies seven charges of indecent assault on a ten-year-old boy, alleged to have taken place at Skegby Hall around 60 years ago.
Anthony Brown told a jury at Nottingham Crown Court he had known Young for 64 years, first meeting him in 1953, aged nine, when Young was teaching in his first job at a school in north London.
He described Young as a “good teacher” and a “lovely man”, who took an interest in him even though he was badly behaved.
Young later met his parents and became a family friend, sometimes visiting for holidays and “sleeping in the same room as me, in separate beds.”
“Nothing inappropriate happened,” Mr Brown said. “He took awkward kids under his wing.”
He said Young took him out on day trips and they had remained friends ever since.
Young, of Burton Stone Lane, York, told police it would have been impossible for him to commit the offences, which include gross indecency and sexually abusing the boy in the bath and in bed.
On a video shown in court, the alleged victim told how he was subjected to a series of indecent assaults over the three years he was at Skegby Hall, where Young was a teacher.
The man, now in his 60s, said Young took great enjoyment in washing boys and would climb naked into his bed when he was alone in his room, while the touching would happen regularly at bath-time.
The man, who cannot be named for legal reasons, said he had reported the behaviour to the school headteacher, but was told to go away and “not be a silly boy”.
He had kept quiet about his ordeal for decades until the subject of historical abuse had become a public debate.
Young was interviewed as part of Operation Equinox, an investigation into cases of historic child abuse.
He told police he had no memory of the complainant and said he had been single all his life and had never had a sexual relationship as he suffered from a genetic condition he did not want to pass on.
He said he had a normal sexuality.
He said he could remember staff during his time at Skegby but not that individual pupil.
Young said there were 42 boys aged 8-13 at Skegby, when the offences are alleged to have happened, and they were resentful of authority.
The trial at Nottingham Crown Court continues.