There is a teacher at my school who is adored by students and staff. He’s a dedicated and efficient educator with years of experience who once taught some of our pupils’ parents. The school benefits from his expertise daily, from the way he handles tricky content to how he manages difficult behaviour. In many ways, he is irreplaceable.

Sadly, we’re losing him. Forced to record data that’s never looked at and deliver subjects focused on rote-learning that leaves students uninspired, he feels unable to do the job he signed up for. But he’s just one of the older, more experienced teachers leaving the profession.

The average age of teachers is falling. In 2013, the OECD teaching and learning international survey found the average age of teachers in secondary schools in England was 39 – almost four years younger than the global average. Government figures show that the number of older teachers has dropped significantly since 2010.

The impact of replacing older, experienced teachers with younger, inexperienced individuals is difficult to measure. But it’s clear that students, younger teachers and the wider profession will be affected.

In a few years’ time, I’ll be a teacher of above average age for England, with the corresponding seniority and expectation of expertise. Yet I feel hopelessly unprepared to become the new “old guard”. My students enjoy their lessons and do well enough, but I rely on advice from older colleagues in my practice.

Nuggets of wisdom – about how to arrange my classroom on the first day of term and then adjust it for behaviour, for example, or the level of detail needed when teaching certain topics – have made a big difference to how I work. Their insights have helped me make my lessons more meaningful to students.

There is an experience vacuum being created in our schools that robs junior teachers of the role models they need to help them improve. Formal teacher training is the equivalent of being told how your parachute works before being chucked out of a plane at 12,000 feet. Becoming a teacher takes years: it’s a lifelong apprenticeship, with best practice passed from experienced colleagues to new recruits.

Newly qualified teachers have many strengths, such as energy and adaptability, but they’re not experts in the art of teaching – and nor should they be expected to be. I fear that by losing our top tier of experienced professionals, overall quality will drop, generation on generation.

The only way to reverse the declining average age of teachers is by changing the culture of the profession and giving people incentives to stay in the job. But any real shift will come too late for teachers like me, who have enjoyed only a handful of years in the presence of colleagues with decades of experience. Without their guidance, confidence and expertise, we’ve got a knowledge gap about what works in teaching – and that’s a problem.

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