Secret weapon that must stay secret
However, suggestions that the scheme, which was phased in over the past four years, should be linked to teachers' pay were seen as untenable and likely to undermine appraisal.
Staff would become suspicious, defensive, and unwilling to take part in classroom observations.
Headteachers in Kent's secondary schools regarded confidentiality as central to the success of appraisal.
"It is fundamentally built into the scheme. I only see the reports which I write or my own appraisal report by a fellow head," explained Peter Walker, head of the Abbey School in Faversham which is seen as a centre of good practice.
"It helps staff to look inwards, it can identify needs which may need putting right and which might help the individual and ultimately the whole school.
"But senior managers must be well briefed to respond to what appraisers are saying otherwise the whole service falls down. I do not see how a good appraisal system can run unless it is linked to the school development plan, we regard the two as intertwined."
Appropriate funding and adequate time for the local authority to train appraisers were also seen as crucial, according to heads who spoke highly of the support provided by Kent's education department.
John Edwards, headteacher at Harvey grammar school, Folkestone, said appraisal had broken down classroom barriers and eased tension among staff who previously regarded observation as a threat.
"I think classroom observation is important and appraisal has gone some way to facilitate it. It is far more than this, however. There are times when some members of staff express a wish for things which cannot be delivered either because they are not the right person for the job to which they aspire or because funding is not available, so there is an element of swings and roundabouts in the whole thing."
One head who wished to remain anonymous was sceptical about the benefits and cost-effectiveness of statutory teacher appraisal. "It has not made very much of an impact upon us quite honestly and I doubt if it has made much of an impact upon classroom practice," he said.
Informal appraisals had taken place at the 500-plus boys school for years. The introduction of the statutory scheme had merely formalised what was already in existence and the cost was unnecessarily high.