When all is said and done, leadership comes down to performance. You do not become an excellent headteacher simply by talking about it, although the gift of the gab would to be an essential prerequisite for the job.

Heads demonstrate their prowess through high-profile activities such as school development planning and curriculum design. But there is a world of difference between the efficient manager and the effective leader. For me, headteachers become leaders by the way they behave in defining moments, those critical occasions when they have to deal with people under pressure. Such times can forever shape the way others see you.

Take three examples. Handling weak and incompetent teachers is one of the most illuminating. It is easy to talk tough and, yes, it is necessary to be in-tolerant of failure because pupils’ life chances can be affected by poor teaching. But even teachers who recognise incompetence in their colleagues will watch carefully to see how the head handles such a situation.

It involves more than going through the formal procedures in consulting with the unions. It is about treating people with dignity and respect. It is recognising that being told your career may be over is a shattering experience.

As one headteacher said: “I will always treat teachers the way I would want to be treated if I was in such a situation.”

It is a test of your resolve if you can show that you are prepared to promote high standards but, at the same time, treat people with common decency and humanity.

Another important test comes when you deal with the promotion prospects of others. It is always painful when a star on your staff tells you that they are applying for a head of department job in another school. Yet the best headteachers will encourage colleagues to seek promotion. They will see endless possibilities as new recruits arrive.

How you react reveals a lot about you: if you are churlish and can only think of the problems that will befall you when a good teacher leaves, you will not earn yourself any credit. Small-mindedness can define you forever. Not only that, gone forever is the possibility that your star teacher will become an ambassador for your school once they have moved on to pastures new.

A third area for you to show leadership is the way in which you handle the personal difficulties of your staff, be it a family crisis, the death of a relative, a relationship problem or whatever. The best headteachers recognise that you cannot neatly separate the personal from the professional. Certainly, any head has to be mindful of the impact of staff absence on pupils’ learning. But how many times do heads lose their staff by failing to go the extra mile in helping out a teacher who is in difficulty? What a contrast there is between “Take as much time as you need” and “This really causes me problems”.

Such moments rarely make the headlines in the management textbook. They are not always easy to analyse and the decision-making process that accompanies them does not always have a firm evidence base to support it.

In a time when everything is subject to substantial analysis and has to be capable of being taught, defining moments expose the real you. Processes and procedures may denote you as a manager, but your behaviour with people will reveal your leadership qualities.

* David Bell, a former headteacher, is director of education and libraries with Newcastle City Council