Marjory Condon, the former headteacher of Kilburn Park School in Brent, north-west London, was found guilty of unacceptable conduct by England's General Teaching Council (GTC) this week. She was criticised by a disciplinary committee for allowing her son to run his company, Liberty Moon, from school premises, using the school's address and phone number. He provided services to other local schools and invoiced them for labour and equipment.
Mrs Condon also failed to declare a conflict of interest during meetings which discussed the salary of the deputy head - who was also her husband.
The disciplinary committee's judgment stated that her loyalties had been divided between the school and her husband and son: "She and her family devoted much of their lives to the school."
The committee cleared her of accusations that she had created a furnished living area in the school for her own benefit. Instead it accepted her explanation.
"I slept regularly at the school to fend off burglars," she said. "It is quite ridiculous to say it was for my benefit - I was so anxious about it. It was a real hardship and very dangerous - I have stopped many burglars."
The Office of the Deputy Prime Minister had commended Mrs Condon in 2004 for her dedication to educational attainment, because of the school's high test scores in a community with many underprivileged children and asylum seekers.
Mrs Condon told the hearing that she had worked 12 hours a day, and had not taken a day off in 14 years. "Working on the school was a labour of love," she said.
Mrs Condon, who has since split up with her husband and been dismissed by Brent Council, said she would not apply for headship again but hoped to continue teaching, either in a prison or in a voluntary capacity overseas.
However, John Christie, Brent Council's director for children and families, said the reprimand imposed by the GTC was too lenient, and she should have been struck from the teaching register.