Use of references and personal knowledge of candidates in interviews for places on courses leading to the National Professional Qualification for Headship varies significantly across Wales, according to an external evaluation of the selection process.
In one LEA, there was no female representative on the interviewing panel, and in three there was no one from the secondary sector, which had a "deleterious effect" on discussions, according to the report by consultants TribalPPI Group.
And while most people with personal or professional knowledge of a candidate rightly "sat out" of discussions, LEA advisers' inside knowledge was sometimes used to decide borderline applications.
Such inconsistencies jeopardise equal opportunities for candidates, with some local education authorities identifying far more eligible candidates than others.
For example, last year in Blaenau Gwent only two of eight NPQH candidates were found to be eligible and were funded for the course, and only six out of 11 in the Vale of Glamorgan. But Gwynedd and Ceredigion put forward all their candidates.
The Secondary Heads' Association Cymru warned of feelings among some senior teachers that who you know can matter more than what you know when it comes to getting an NPQH place.
The qualification became a requirement for all first-time headships in England in April. The Assembly government is hoping to make it compulsory in Wales from September 2005. More than 500 Welsh heads already have the NPQH, according to the General Teaching Council for Wales. The evaluation of the NPQH selection process found interviewing panels were generally thorough and fair. But practice varied across Wales on use of references, professional knowledge of candidates, and anonymising applications.
The consultants' report recommends better monitoring of the interview process, to ensure greater consistency between LEAs and "improved equity for applicants".
Interview panels should have at least four members plus the chair, possibly including an Assembly government nominee, and more guidance should be issued.
Brian Rowlands, secretary of SHA Cymru, said its members were sometimes left bemused by why some NPQH candidates were selected over others.
"It's a question of whether it's who you know rather than the consistency of judgments about your own abilities. We are concerned that there should be equal opportunities for every candidate," he said.
A Welsh Assembly spokesperson said: "We are acting on all the recommendations in the report but we have already made the commitment that anyone who wishes to pursue the NPQH will be able to do so in advance of it becoming mandatory because the funding has already been provided."