Susan Barnard now faces being the first teacher to be struck off since laws were changed in 2006.
At the hearing yesterday, she admitted failing to plan coherent teaching programmes, failing to communicate clearly with her pupils and failing to manage pupil behaviour.
Her case came before the General Teaching Council Scotland (GTCS) – the first time that the professional body has considered a case of competence of a teacher.
Mrs Barnard, 55, had already been sacked by Perth and Kinross Council amid concerns about her performance at Coupar Angus, Comrie and Arngask primaries, between November 2003 and December 2006.
Her lawyer, Andrew Gibb, said Mrs Barnard was currently doing supply work for another local authority and hoped to retain her teaching registration when the case comes before the committee again on 3 December.
"Clearly, she's extremely concerned about what the future holds for her," he said.
But Mr Gibb said she decided yesterday, after a lot of thought, that she would accept the charges against her and hopefully present compelling evidence in mitigation which will enable her to keep her registration.
He added: "Mrs Barnard has been treated very fairly by Perth and Kinross Council and the GTCS and she hopes to keep her registration.
"She has been doing supply work in another area and hopes to continue with her career if she retains her registration."
GTCS lawyer Robbie Burnett told the committee that "despite significant management support over an extended period of time to address areas of concern" in her performance, she failed to meet the standards required. As she left the hearing, Mrs Barnard bowed her head and refused to make any comment.
Mrs Barnard was born in Manchester but qualified as a teacher in New Zealand and has been working in Scotland for the past 25 years.
Gordon Smith, from the Association of Headteachers and Deputies, has demanded that more cases are brought forward to GTCS.
He complained that until now, incompetent teachers were simply moved to another school because of the "complex and sometimes Byzantine" process of bringing a case against them.
He said: "I wouldn't wish this on anyone but we have to realise this is an issue in Scottish education that perhaps we've ignored.
"If you were an employer with nearly 50,000 staff, you would probably assume that one to 1.5 per cent had competency difficulties, so for this to be the first case to come forward is surprising for everyone. Imagine it was your child that was in that class and a teacher with 10 years' experience will have perhaps ruined the education of 300 children."
Until the laws were changed in 2006, teachers could only be struck off for criminal or serious unprofessional behaviour, not simply for the quality of their teaching.
The law-change brought Scotland into line with practice in England and Wales, where around 10 teachers a year face losing their registration due to incompetence.
ANALYSIS: Grasping the nettle of discipline
IT MAY come as a shock to parents who expect their children to be well taught in a disciplined classroom, but teachers know that, until recently, they had to do much worse than fail to control pupils to be ousted.
The vast majority of teachers do a good job under circumstances which would test many captains of industry. However, every school has its weaker elements and for generations the profession has shilly-shallied about getting rid of incompetent ones. Why?
Inevitably, there is a financial element. But, ultimately, there has been a gross reluctance on the part of local authorities to take on the unions, or to admit they have made a mistake
Private sector schools have been much more prepared to tackle competence, even if it has had a serious effect on their bottom line. It is, therefore, to be welcomed that Perth and Kinross has had the courage to take the ultimate sanction.
Whether the General Teaching Council should remove someone in this position from its register is a moot point. But ultimately its members have to ask: "Would I want this teacher to be in charge of my child?" If the answer is "no", its course of action seems quite clear.
Let us hope other councils follow the Perth and Kinross lead. If they do, our pupils will benefit enormously.
Frank Gerstenberg is the former head of George Watson's College.