Linda Walker, 48, is claiming unfair dismissal from her £30,00-a-year post teaching children with behavioural problems.
She was sacked after being jailed for affray and possessing a firearm after confronting youths who she said had plagued her family.
But the headteacher of the school told an employment tribunal in Manchester today that it would not be possible for the school to re-employ her
Almut Bever-Warren is current head of New Park High in Eccles, Salford, Greater Manchester - a special school for pupils aged 11 to 16.
She sacked Mrs Walker last July following a disciplinary hearing after she was jailed for three months at her trial at Manchester Crown Court.
Ms Bever-Warren said working at the school was stressful and challenging because of the nature of the pupils.
Teachers should be role models and "remain calm" despite provocation from pupils and it was important to teach them how to function "without taking the law into their own hands," she added.
"I believe it would be untenable for Mrs Walker to advise pupils in anger management because undoubtedly pupils would question her ability to tell them what to do."
Ms Bever-Warren said the school had many, "unpredictable" pupils and she could not afford an "unpredictable member of staff".
She added: "There are a number of reasons why it is impossible for me to employ Mrs Walker."
Questioned by Cliff Anderson, regional officer for the NASUWT, representing the sacked teacher, the head accepted Walker had been provoked.
She conceded Mrs Walker's work during her 25-year career had never before fallen below expectation.
But she added: "The problem, I thought, was whilst I accept there had been no indication of Mrs Walker not fulfilling her role to a satisfactory standard, that one slip was one too many.
"The young people you are dealing with at New Park are the same type of young people she felt harassed by."
Mrs Walker, from Urmston, Manchester, was sacked by the head after council bosses in Salford held a disciplinary hearing last May. Her subsequent appeal also failed.
She was found guilty of affray and possessing a firearm with intent to cause fear during the incident in August 2004.
Mrs Walker was given a three-month jail sentence last March but was freed 36 days later after Appeal Court judges quashed her sentence, but ruled her conviction should stand.
The trial heard that she lost control and used the gun after her family and home were plagued by yobs.
Her case attracted widespread support and much sympathy for a teacher who had stood up for her family by confronting a teenage gang.
She was dismissed after her conviction. The council argued that by getting a conviction Mrs Walker had committed gross misconduct and was unfit to be a teacher.
The employment tribunal has the power to order reinstatement.
The hearing is scheduled to last four days, and Mrs Walker is expected to give evidence tomorrow.
Copyright Press Association 2006.