An industrial tribunal found Mark Eales, Doncaster's education director, had acted in an insidious way by suggesting the heads recommend that Tony Brookes, head of Thorne grammar school, step down.
They passed on the director's message to Dr Brookes, who then confronted Mr Eales and resigned at the end of 2002.
Dr Brookes this month won an unfair dismissal claim against Doncaster council on the grounds that the director had acted improperly.
The tribunal said that Mr Eales had not specifically instructed Bob Johnson and Martyn Vickers, then heads of Don Valley high and Danum school, to act as his messengers. But it said: "We also found it clear that those gentlemen were left in no doubt that this is what the director of education required them to do."
The tribunal was also critical of Mr Eales's behaviour during his meeting with Dr Brookes. It acknowledged that reports conflicted over whether Mr Eales had acted in a bullying manner, but said the meeting had left the head shell-shocked and that he was devastated by the council's treatment.
Dr Brookes, 56, believes the council wanted him to resign because he had opposed attempts to close his school's sixth form and because the education authority planned to turn Thorne into an academy. It re-opens in September as Trinity Academy, with sponsorship from the Vardy Foundation.
Mr Eales has denied the claims. He said he wanted Dr Brookes to retire because only a fifth of pupils at Thorne grammar gained five or more A* to C grades at GCSE in 2002 and because inspectors found the school had serious weaknesses in 2000.
However, Ofsted was forced to apologise to Dr Brookes after problems with the inspection were revealed. The school was also taken out of serious weaknesses at a second inspection, only five weeks after Dr Brookes resigned.
The tribunal, which will meet next month to assess damages, ruled that Dr Brookes was 25 per cent to blame for his dismissal because he had failed to prepare fully for the original inspection.
Dr Brookes, now working as a science teacher at Corpus Christi Catholic college in Leeds, said he would be contesting the claim that he was partly responsible, but was otherwise pleased with the ruling.
Doncaster council said it could not comment on the case because it was considering an appeal.