Roger Caffrey is charged with three counts of rape and 14 indecent assaults in Nottinghamshire dating between 1978 and 1995.
Sixteen of the 17 charges involve girls under the age of 16 - some thought to be as young as nine.
Mr Caffrey, who taught at 10 schools in the county, denies all the charges.
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Nottingham Crown Court heard Mr Caffrey's teaching career spanned more than three decades from 1966.
He told the court he taught all subjects, and later became a specialist in helping schools through Ofsted inspections.
The 70-year-old, now of Sandesquoy, Tankerness, Orkney, is accused of raping two girls at his then home and touching pupils while they read aloud in class or touching them in a store cupboard in the classroom.
Mr Caffrey admitted that he would put his arms around pupils' waists, or, on some occasions, pat them on the "side of the buttock" to praise them after they read in front of class.
"It just seemed the natural thing to do," he said. "It was encouragement back in those days.
"Obviously it's different today. There was nothing sexual [about it]."
Mr Caffrey said one of his former pupils - who has accused him of raping her - was the kind of person he would have liked his daughter to have been.
"She was very athletic and she'd got a lot of guts, grit and determination," he said.
"I had no sexual feelings [towards her]. I had no sexual feelings towards any of my pupils."
The jury heard Mr Caffrey, who has been married three times, left his first wife while she was pregnant to live with a member of school staff.
He admitted having another "brief affair" with a staff member at a primary school where he worked until 1984.
"I was a womaniser," he said. "I'll plead guilty to that."
The trial continues.
A former teacher accused of rape and sex abuse told a court he did pat pupils "on the side of the buttock", but denied any sexual intention.