Schools are often forced to turn to recruitment agencies, some of which offer an exorbitantly priced and poor quality service, trying to offload candidates on their books "regardless of their merits", the National College for School Leadership says.
The college has put out guidance to help tackle the head shortage that has hit Catholic and London schools particularly hard.
It says: "Governing bodies should have a long-term plan in place for headteacher succession, keeping the current head involved, and identifying possible internal recruits." The college cautions against relying on agencies: "The fee may be considerable and not all providers in this new market offer the same level of quality or attention to your individual needs." One north London school, Henrietta Barnett girls, says it paid about pound;30,000 to recruit a new head - approximately pound;20,000 of that to a headhunting firm.
Stuart Lester, chairman of the governors, says that in their case the recruitment firm had got results and headteacher Oliver Blond started work at Easter.
"We needed a good head, and we had to get one, although some of us swallowed hard at the cost," he said. "Many schools would not have been able to afford it."
* Advice on recruiting headteachers and senior leaders can be found at: www.ncsl.org.ukresearchresearch_activitiesrecruitingleaders