Internal promotions, where the post is available only to people already working in the school, are much harder for everyone to deal with than the normal "open advertisement" appointment. Even those can be painful for the internal candidate, if he or she is not appointed, and for the appointing panel who have preferred a stranger. But this is nothing compared with the "internal candidates only" promotion.
Failure to achieve a promotion in this way is a public form rejection which can undermine a teacher's confidence for years.
One former colleague continued to blame me for his failure to achieve a post four years earlier - despite later success and his acceptance that the person appointed had done a good job.
Internal promotions mean everyone knows who's applied and each staff member has his or her own view of the best candidate. It's impossible for the appointing panel to please everyone and so it must have the courage to please itself.
But unsuccessful candidates are entitled to an explanation - which makes life difficult for the head or other senior person charged with de-briefing. It is insulting to a colleague to suggest he or she didn't get a job because "X was better in the interview". And often difficult choices made for reasons not directly connected with the post - for example, the "knock-on" effects of appointing one person rather than another.
The disappointed candidate, however, demands to know "what's wrong with me" and the answer "you didn't lose the job, X won it", while probably true, sounds too glib. Many vow never again to apply for a post in their own school.
For the successful candidate, too, life after internal promotion is not always rosy. One teacher, who never believed herself the best candidate, was so surprised by her promotion she became convinced she was a pawn in some political manoeuvre by the head and mistrusted everyone's reaction to her for most of the time she held the post. With an internal appointment, too, it's harder to celebrate success for fear of rubbing it in for the other candidates.
The irony is that internal promotion ought to be a key strategy within a school's staff development policy. Both for the young teacher seeking a first step on the promotion ladder and the experienced middle manager unable or unwilling to move elsewhere, a promotion within his or own school should be a real career development opportunity.
Heads and governors should also see nurturing talent and helping colleagues to progress as an important part of their management function. And yet few, except perhaps the head recently described as "a fierce promoter of talent", relish the disturbance it can cause.
Part of the problem is our commitment to open competition for posts. This means that although most heads will actively discourage really inappropriate applications, any one post may produce a number of candidates - particularly in these days of limited opportunity within schools and static house markets outside.
The head will probably have a favoured candidate - indeed new posts are often created with a particular person in mind - but must treat all others even-handedly and be prepared to be surprised by someone whose ideas about the work may have been hidden.
Internal politics - often quite benign and not nearly as devious as some people might believe - may also play a part in appointments but cannot generally be admitted.
Schools have tried different ways through the internal promotions minefield, including short-term rotating posts and having all appointments made by a panel of the candidates' peers. In the end, however, there are only two choices: either don't do it or accept the inevitable consequences. Which is also the position for potential applicants.
By applying for an internal promotion you put your head on the block. And, like everyone in that position, the temptation is to invest the situation with too much significance. For the period from advertisement to appointment you may think of little else and allow your obsession to get in the way of other work. Colleagues will want to advise or offer their support, other candidates may feel embarrassed in your presence, the head and senior colleagues may become distant as they try to maintain neutrality. And you may wonder if it's all worth it.
If you decide it's not, there is then the tricky problem of withdrawing. Supporters will be disappointed, denigraters smug and senior staff confused about your career motives. Any future indication of interest in an internal post will be treated with caution.
Therefore, think carefully when the internal promotion ad goes up; decide if the job's worth the aggravation; and, if it is, be prepared to ignore all advice to the contrary. After all, nothing lasts for ever - not even the pain of being rejected for a post in your own school.
Mike Fielding is principal of The Community College, Chulmleigh, Devon