The former deputy head of John Ruskin School, Coniston, told an employment tribunal this week that he was forced out of his job by the head teacher.
Stuart Lymath, 57, took early retirement after a period off work with stress.
He claims he was constructively dismissed from the position he had held since 1984.
Cumbria County Council denies constructive dismissal, arguing that Mr Lymath had been unable to keep pace with the changes in education and the roles of senior staff.
The tribunal heard that a new head teacher, Mike Major, arrived at John Ruskin in September 1998.
Mr Major told the hearing that, on taking over, he considered Mr Lymath's numerous roles were inappropriate for a deputy head teacher and were not sufficiently "managerial."
One example, he said, was Mr Lymath's position as school calligrapher - writing certificates in copper-plate style - which was time-consuming and, he believed, a trivial job.
"A clerk does it now, taking an hour a week, on a computer," he said.
Mr Major, during a full day giving evidence, said he asked all his senior staff to clarify their roles.
Mr Lymath had a considerable number of responsibilities, including head of science, examinations, secretary, finance manager, information technology manager, welfare and discipline and buildings and was active in the PTA.
While it was not one of his duties, he compiled the annual school timetable.
Mr Major said he removed his responsibilities for calligraphy and head of science and asked him to take on the role of assessment manager.
"Assessing and monitoring children's progress is part of every teacher's basic training," he said.
"Most deputies would give their right arm to do the job of assessment manager but Stuart didn't do it and I was very disappointed."
Mr Major, who denied suggestions that he had delegated too much responsibility to Mr Lymath, over-burdening him with work - some of it trivial - told the hearing: "I consider I relieved him of the menial tasks that had built up over time and gave him a meaningful management role."
He agreed with Mr Lymath's counsel, Christopher Roy-Toole, that the deputy did not have a written job description but said he had drafted one and been unable to discuss it with Mr Lymath, who was absent through illness.
And he claimed other staff, aware of Mr Lymath's shortcomings, would do some of his work for him.
"In many cases, he quite vehemently refused to do things I asked him to do," he said.
Mr Lymath, of Ambleside, told the hearing: "The head's attitude towards me was hostile, dismissive and cold and he had a tendency to order me to do things rather than ask, or discuss them."
Events in their stormy relationship led, in the summer of 1999, to the governors' involvement.
Mr Lymath rang Mr Major at home, then went to see the chair of governors.
At issue was the compiling of the school timetable, which had been taken out of Mr Lymath's hands.
The deputy also complained about Mr Major.
The head teacher had an already-scheduled meeting with the county's Schools' Inspector and, after discussing the situation, it was decided to hold a "capability review" of Mr Lymath's work.
Mr Major denied suggestions by Mr Lymath's counsel that the review had been provoked by a staff letter to governors, criticising the head's working methods, or by Mr Lymath's protests to the chair of governors.
The initial, and only, meeting was held between the head, his deputy, another senior teacher and Mr Lymath's union representative to "identify problems and consider whether they can be tackled."
The "final straw" for Mr Lymath came in October 1999, following an inspection of the school by OFSTED.
At a staff debriefing, Mr Major quoted the OFSTED inspector as directly criticising his deputy's management capabilities.
Other teachers present told the hearing it created a "terrible atmosphere" and was "a grave misjudgement by Mr Major."
Summing up on behalf of Mr Lymath, Mr Roy-Toole told the three-man tribunal panel: "Mr Lymath's position was undermined and made unworkable by Mr Major, who over-delegated his own functions, unilaterally changed his job, never gave him an adequate job description, failed to support him when he was suffering from work-related stress and invoked the capability process in bad faith.
"Clearly he resigned from his job in response to the head's behaviour to him."
Counsel for the county council, John Dowse, told the hearing: "For many years, while a kindly and helpful man, Mr Lymath was not keeping up with the changes in the teaching profession.
"He spent a lot of time doing things deputy heads shouldn't do in the present age.
"He found it difficult to come to terms with the new requirements of the education world.
"He took advice and retired.
He made the decision to go.
That is the case."
The tribunal reserved its decision, which it will give in writing to both parties, in several weeks.
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