“Drop-outs cost millions” is a pretty scary headline in our cash-strapped education system (TES, July 27). According to data from the Training and Development Agency for Schools (TDA), one in five PGCE trainees in shortage subjects fails to qualify, and many who do get through decide not to teach. Some universities are struggling to fill places and as a consequence are accepting lower-quality applicants with less commitment to the profession. So what’s going on?

Teacher training is a great interest of mine. For two hours a week I work with would-be teachers. I listen to them, guide them through the storms, and try to inspire them to understand that they are entering one of the most important professions in the universe. Sometimes, in a magic moment, I see the sparkle of belief in their eyes, a flame lights and a shining new teacher is launched into the profession.

But the downside is that we, too, have our share of drop-outs. I expect the TDA is already moving on to the next stage of its inquiry and will soon provide us with data to explain why so many trainees fail to make it. Until then, I’d like to offer up my own research methods, and my current findings. When my PGCE students decide to drop out of their school practice, I block the door and won’t let them leave until they tell me where it’s all gone wrong. Their response is always interesting. Here are the five most common reasons for their premature departure; in rank order.

1. Too much work. It is a crushing blow to graduates, especially the younger variety, that their social life is suddenly swallowed up in such a range of ways, lesson planning being the worst cause of misery. Perhaps even more devastating is the reality that there is not enough time to sleep “I just can’t do this any more.”

2. Unrealistic expectations of pupil responses and behaviour. Another body blow, this time an attack on self-esteem (already made fragile by the point above) when there is the horrid realisation that children often do not respond in the ways expected of them “They don’t listen when I try to teach!”

3. A massive underestimation of the bigger picture. Some newcomers have a touching but fatal naivety about all the other factors that affect schooling, such as catchment area, inadequate parenting, Ofsted inspections, league tables, curriculum restraints “I can’t take on the world!”

4. The lure of an easier and better-paid life elsewhere. For example, the maths trainee who opts out to take up a career in accountancy, or the bright spark in ICT who can command much more money and, more importantly, instant respect from a firm such as IBM “Sorry, but it’s the truth!”

5. “Personal reasons”. These are usually tangled up with the points above and often culminate in a partner’s or spouse’s ultimatum “Your teaching practice is ruining our relationship something’s got to give!”

None of these points will surprise anyone. But what is startling is that we continue to attract so many of the wrong people into the profession. In Finland, the top third of graduates go into teaching. I wonder what their drop-out rate is and what their selection procedures are?

In the meantime, I will continue to remove my foot from the door when my questions have been answered, and I will wave our drop-outs on their way. They have undoubtedly saved themselves from making a terrible mistake, but so has the teaching profession. It often feels like a lucky escape for all of us.