I don’t quite know when it happened, but at some point I became an experienced teacher. In fact, I’m often one of the most experienced teachers in the room.

I sometimes get to visit other schools for Inset days or CPD sessions, and will start by asking how many people in the room have been teaching for fewer than five years, and how many for more than 10.

The first question inevitably generates a sea of hands in the air, but the second gets only a few. At the age of 38, and with 16 years in the classroom, I am often the oldest and longest-serving teacher in the room.

This increasingly common experience has left me with two questions. First, how did this happen? Where have all the experienced teachers gone? Second, does it matter? Just how important is experience, anyway?

The Department for Education’s workforce survey shows that nearly 10 per cent of teachers left the profession in 2018. That’s 42,000 teachers in all. Of these, only 6,300 retired. The rest simply moved out of teaching, presumably into another career.

This high level of teacher drop-out leaves UK teachers an average of five years younger than the average for Organisation for Economic Cooperation and Development (OECD) countries, and four years less experienced.

Only 18 per cent of teachers stay in the profession after the age of 50. No wonder I often feel prematurely old standing in front of a roomful of teachers.

The reasons for this exodus from the classroom are not hard to piece together. The OECD found that working hours for UK teachers were the second highest in the world, just behind Japan, and that more than half of secondary school teachers describe their workload as unmanageable.

The government’s principal solution seems to have been an attempt to boost teacher recruitment by offering training bursaries, especially in the ever-growing list of shortage subjects. There have also been recent announcements that the starting salary of teachers will be increased, all with the aim of making teaching a more attractive profession.

This is very welcome, but it only deals with one part of the problem. We are pumping more teachers into a system that spits them out the other end just a few years later. According to a report by the Institute for Fiscal Studies in 2016, it costs on average £23,000 to train a teacher. Yet 40 per cent of those who train leave the profession within five years. This constant need to replace teachers is an expensive business, and my concern is that there are even greater problems brewing.

In their book The Teacher Gap, authors Rebecca Allen and Sam Sims show that, once teachers qualify, they face a very steep learning curve. In the first three years of teaching, they become much more effective teachers in terms of pupil outcomes.

In these early years, they are taken from a (usually) very supportive and structured training year and suddenly thrust into an environment where they are expected to take on a lot of individual responsibility: for their classes; for dealing with behavioural issues; for contacting home and writing reports; for writing lessons and sometimes entire schemes of work; for assessment; and for performance management. Never before has the term “sink or swim” seemed more appropriate.

After three or so years of rapid improvement, teachers tend to plateau, or to see pupil outcomes rise much more slowly. We reach the point at which we are just about competent enough to relax slightly - but by then, many teachers are handing in their notice and heading off into the sunset.

Not only is this a huge waste of money for the state, which has trained and invested in these teachers during their learning phase, but it is a personal tragedy for those teachers who have thrown in the towel after several years of incredibly hard work.

But what about for the profession as a whole? Does it matter that teachers are leaving before they’ve had a chance to acquire any sort of experience?

Running on autopilot

The idea of expert teachers has been explored by the researcher David Berliner in papers such as 2001’s “Learning about and learning from expert teachers”. He suggests that there are a number of differences between expert and novice teachers, and that these differences are highly significant.

Berliner suggests that expert teachers are formed through a combination of talent (innate ability), deliberate practice and context, and that the last two are by far the most important. Developing expertise in something takes time. We need to do the same thing over and over again to the point that it becomes automated.

This is a defining characteristic of an expert. It means that they don’t need to think so hard about what they are doing, as many of the micro decisions in the classroom are made on autopilot. How should you respond to that pupil calling out? Who should you direct this question to? How can you help that pupil who is struggling with the work? A novice teacher will have fewer experiences to draw on to guide the best course of action. The expert, meanwhile, will subconsciously tap into prior case studies of similar situations and act accordingly.

Expert teachers are also more responsive. Having taught the same topic a number of times, and therefore feeling confident with the subject matter, they are able to act in the moment to address misconceptions or deal with errors as they arise. They are less tied to following a particular lesson plan and getting through a number of preplanned activities.

Teachers’ expertise is also important for pupils in a class, and it is very context-dependent: change the context too much, such as putting an experienced teacher in front of a new group of children, and you lose a lot of that expertise. Experienced teachers are quick to pick up on the nonverbal cues from classes that they teach, and this enables them to respond quickly to their needs. Novice teachers are less able to do so.

This ability to act automatically makes the job a lot less cognitively taxing: you don’t have to think so hard. It also takes less time to do things once you know what you’re doing. Lesson planning and feedback is quicker if you have taught similar lessons and marked similar work dozens of times before. We could therefore define expert teachers as those who have been teaching long enough and - importantly - well enough to make it look easy.

This means that expert teachers should have more time and energy to devote to other things. Schools need expert teachers to review and update the curriculum, mentor new teachers and work on whole-school priorities, away from the immediate demands of the classroom.

Erosion of teacher autonomy

We are already seeing a reaction to this lack of expertise in schools. It is becoming increasingly common for multi-academy trusts to have a small group of highly experienced teachers writing and resourcing a common curriculum with common assessments, to be followed by teachers across the entire group of schools.

I have visited schools in which a staff body, made up almost entirely of newly and recently qualified teachers, was expected to follow to-the-letter lesson plans written by a small group of senior leaders. While it makes sense to lighten the load of new teachers so that they can practise the art of teaching a lesson, we risk losing teacher agency and classroom autonomy.

Interestingly, however, because experts have a greater range of experiences to call on, they may take longer than novice teachers to reach a decision: they simply have more information with which to make one. However, once made, the decision is more likely to be the correct one.

So, if a new initiative is announced and, a day or two later, an experienced teacher knocks on the door to express a concern, that concern is probably worth listening to. We need expert teachers who have been in education long enough to provide a voice of reason and experience. It is useful to have someone who was around the last time an initiative was tried, who can explain why it failed then and suggest what should be done differently now.

Expert teachers act like a living archive of previous policies and strategies. It is very easy to roll your eyes at the old codger in the corner of the staffroom who mutters “it all comes around again” every time someone presents something shiny and new. But it is usually worth learning from the mistakes of the past to avoid repeating them.

Recently qualified teachers can bring a huge amount to the job, but they can’t replace years (and even decades) of experience and careful practice. Without our expert teachers, our profession will be a poorer one - and one that’s more susceptible to the erosion of professional agency and autonomy. We should act now if we want to save this most endangered of creatures: the expert teacher.

Mark Enser is head of geography and research lead at Heathfield Community College. His latest book, Teach Like Nobody’s Watching, is out now. He tweets @EnserMark

This article originally appeared in the 120/27 December 2019 issue under the headline “We’re making it hard to make it look easy”