Ministers want bad teachers sacked within a month, instead of up to 12 years as the process can now take. But getting rid of a teacher is a complicated business, as a new study has found. Judith Judd, Education Editor, explains why.

Ministers want the worst teachers sacked within a month and they want all bad teachers to go within two terms. But new research published today which found that heads were spending up to 12 years negotiating departures also found that it was a complicated matter.

The first part of the two-year study from Exeter University - the first in Britain to look in depth at incompetent teachers - which has been sent to David Blunkett, the Secretary of State for Education, says: "Anyone who believes that dealing with allegations of incompetence is easy should think again."

The research cites the case of a head who was about to bring proceedings against one teacher to a close. The teacher went sick for 100 days on full pay and another 100 on half pay and the proceedings had to be delayed. Eventually he was given ill-health retirement.

Of the 60 heads questioned, three-quarters had brought cases involving incompetent teachers to a conclusion. The rest were still in progress. About half of the completed cases took between 18 months and two and a half years. Three, all involving teachers who kept returning after periods of sickness, took seven, eight and twelve years to complete. No one was eventually sacked. Seven teachers were judged to have improved, and in most of the remaining cases, the teachers' departures were negotiated. Two remained in their jobs with the problems unresolved and two were given different duties in the same school.

What is incompetence? According to the heads, the study funded by the Gatsby Charitable Foundation says, the most common problem is the inability to keep order. Bad teachers were not just the permissive ones but those who "shouted and harangued children expecting them to sit and listen". Some who knew a lot about their subject had no idea how to make it interesting. Those who did well in one school, could not survive in another. All the cases involved anguish for the heads as well as the teachers. Professor Ted Wragg, the study's director, said: "All the heads said the first duty was to the children but, as managers, their job was also to bring teachers up to scratch and not just fire them the minute they faltered. Under employment law, they are obliged to offer them retraining and a chance to improve."

Teachers, children, parents, governors and local authority officials will be questioned during the rest of the study.