The former Manchester United manager said the "gritty determination" of the formidable Elizabeth Thomson who taught him as a boy rubbed off on him - along with the use of her belt, which is now a prized possession kept at his Cheshire home.
"It's in my study," Sir Alex said, recalling his schooldays at Broomloan Road Primary, Glasgow.
"My grandchildren are terrified of it. Six from that belt and you were in absolute agony. I used to try to draw my hand away.
"But that was the sort of punishment you had if you stepped out of line. In my case, it was usually for fighting in the playground."
Teacher and pupil kept in touch throughout his career as a player with clubs such as St Johnstone, Dunfermline and Rangers, and as a manager with East Stirling, St Mirren, Aberdeen and Manchester United.
"When she died, I couldn't go to the funeral because Manchester United were playing abroad, but months later I received a parcel," he said. "She had bequeathed her belt to me. Her nephew sent it to me with a letter that said, 'You'll know more about this belt than anyone'."
Sir Alex, 72, built a fearsome reputation for disciplining his players - and referees - with his 'hairdryer' treatment.
And though corporal punishment was banned in British state schools in 1987 he fondly recalls his schooldays in the 1950s, when teachers did not "spare the rod" and as a boy from Glasgow's mean streets he stood, hands out, waiting for his punishment from Mrs Thomson.
"Elizabeth Thomson was an inspiration to me," he said. "That's the perfect word to describe her. The area I grew up in, Govan, had one of the highest truancy rates in the city. She came from a different world, really. She was from a middle-class, wealthy family, but she had a raw determination about her.
"When she first got to Broomloan Road Primary, she went round to the house of every student who was not in her class that day and said, 'If your kid isn't in school tomorrow, I'll be back at your door'.
"Maybe 2000 teachers turned the job down, turned down that sort of challenge, but she thrived on it. She improved everyone she touched. She actively sought out challenge.
"The three ingredients to Elizabeth, when I think about it, were personality, determination and energy. Anyone who is in charge of someone else needs those three ingredients. It just won't work without them.
"When I think about her now, I realise it wasn't all about education. Mrs Thomson endeavoured to make you want to be the best you could be.
"Yes, I think there is part of me that comes from her. That determination and that sense of drive. That 'never give in' attitude she had about all her students."
Sir Alex, who recalled his schooldays for The Times Educational Supplement's feature, My Best Teacher, is a patron of education charity Shine, which runs Let Teachers Shine, a competition to fund innovative teacher-led ideas to raise attainment in the classroom.
To apply for a grant of up to £15,000, see: shinetrust.org.uk