Mr Mitchell, the association's outgoing president, appealed for a mechanism to replace teachers who had not broken any rules.
"Not all teachers are excellent. Most are very good, some are good but a minority are awful. As we know from bitter experience it is almost impossible to get rid of an individual who is a poor teacher but who has no other social faults such as alcohol, drugs or an unhealthy liking for young boys."
Mr Mitchell went on: "Few teachers are poor from the beginning. Some simply get tired and exhausted and lose all enthusiasm for the job. The eagerness with which they seek early retirement constrasts dramatically with the lack of energy put into their day-to-day work."
He also claimed that Scotland was beginning to lose its traditional educational consensus and criticised the lack of consultation over a raft of initiatives such as appraisal, student mentoring, national testing and league tables of attendance and results.
"We are now beginning to face the same problems as our colleagues in England and Wales - policy-making by whim, decisions about education based on political needs, government strategies which are blatant media exercises and do not produce a single improvement in teaching and learning for a single child. "
He avoided criticism of Standard grade, Higher Still and 5-14, which were "purely educational initiatives" and "if properly resourced" could ensure Scottish education faced the 21st century with confidence. The amount of consultation over Higher Still set it at total variance with other initiatives. "Obviously, someone got it wrong."
Mr Mitchell also attacked school buildings, which were "cold, uncomfortable, damp, stained, dull and dismal" and which betrayed the signs of decay, rot and neglect which were otherwise only evident in HM prisons.
Teachers had to cope with conditions that would be unacceptable to other professsionals. "When did you last see water pouring through the roof of your solicitor's office? When did you last see an accountant wearing a woollen scarf at her desk? How many GPs have to wipe plaster dust from the top of their computer every morning before starting work?" he continued.
The president's wide-ranging address took a further swipe at the Government when he attacked its lack of action over blatant cigarette advertising at the same time as it told teachers to instruct pupils to say no to drugs.
Mr Mitchell's other targets were employers who complained pupils were unable to read, write and count as well as their predecessors; the press for "trial by headlines"; and those parents too eager to criticise teachers and jump at legal action.