As the school gates open and students flood in with shiny shoes and new backpacks, there's an expectation that teachers should be bursting with enthusiasm to get back to the classroom after their long summer holiday.

The reality is that teachers have mixed feelings as the school year commences.

Some describe dread and anxiety while others say they're hopeful or 'trying to remain positive'.

"I feel better than I did in previous years," an experienced teacher says.

"Our new principal makes our workload more manageable."

Another teacher — mid-career, early 40s — discloses her panic at the thought of a year working with a particularly challenging student.

"I'm not sure how much longer I can do this," she confides.

A graduate teacher, just three years into his career, tells me of his travel plans.

"I'm not going to teach," he explains. "I need a break. I can't face the thought of so much work and all that stress.

"I do love teaching," he smiles ruefully. "Teaching is awesome until you have to do something other than teach, which is about 80 per cent of the time."

Teachers leaving in significant numbers

It's worth considering the fact that many of the teachers who walked through the school gates last year aren't returning this year. And it's a trend we can expect to continue.

Teachers are leaving the profession in significant numbers — the latest figures from the Australian Bureau of Statistics suggest 53 per cent of people who hold a teaching degree do not currently work in education.

And research conducted by the Australian Government in 2014 estimates that 20 per cent of education graduates do not register as teachers on graduating, meaning many teachers are leaving before they've even started.

We aren't investing in our teachers, says Associate Professor Philip Riley. And students will suffer as a result. ( AAP: Dan Peled )

But the specific reasons why teachers leave and precisely how many are leaving are largely unknown.

There is currently no systematic tracking of teachers who leave the profession, let alone analysis of the reasons why they do.

Not only does this impact teachers and kids — disrupting staff teams and school communities, and even impairing student learning — experts say it also prevents education departments from identifying teacher shortages and planning for the future.

So why is it that the job with 'such great pay and so many holidays' isn't retaining its workforce?

'We're going to have a teacher shortage'

Associate Professor Philip Riley from the Australian Catholic University, who is leading research into teacher attrition, says the first problem is that no-one is collecting and coordinating the data on a federal level.

"There are nine parallel [education] systems operating across Australia," Professor Riley explains.

"There's state, Catholic and independent. Each of them are collecting information in different ways, but no one is bringing that information together."

About 40-50 per cent of graduate teachers leave within their first five years on the job, figures show. ( Amy McCosker )

Professor Robyn Ewing from the University of Sydney, who also researches teacher attrition, agrees the current systems for data collection need review.

"There's a huge problem in Australia getting reliable statistics on this issue because most teachers begin as temporary or casual," Professor Ewing says.

"At the moment we're only tracking those that are permanent."

The latest national data from the Australian Government suggest an average of 5.7 per cent of teachers left the profession in 2014.

It seems a fairly innocuous figure, however Professor Ewing argues it doesn't provide any insight into what is happening to teachers on the books.

"Government bodies reassure us that there are thousands of teachers on the list," Professor Ewing says.

"But that just means they're registered to teach. Many of those have taken up other jobs or moved to different systems or are stuck in the casual, temporary cycle.

"In actual fact we have evidence to suggest that we are going to have a teacher shortage."

One figure that adds weight to Professor Ewing's argument is the alarming percentage of those who leave the profession shortly after graduating.

Although the figure varies by locality, about 40 to 50 per cent of our newest teachers leave within their first five years on the job.

These graduates are leaving for various reasons, but similar themes recur: they feel burnt out, unsupported, frustrated and disillusioned.

Many cannot secure permanent, full time employment and so leave the profession to pursue careers with fewer demands and greater certainty.

'Anything is preferable to teaching'

For example, Kate, 30, left the profession several years ago after her first year of full-time teaching, and now works as a freelance writer.

"Of my six close friends who I graduated with [in 2007], only one is returning to the classroom this year," she tells me, before listing off their new careers: blogger, footballer, police officer, priest, publican.

It seems that anything is preferable to teaching.

"New teachers are expected to have all this energy and enthusiasm to make up for our lack of experience," Kate explains.

"But that energy gets drained away. Nobody's supporting us when we're finally in the job."

Teachers are competing for positions and constantly trying to make themselves look highly employable, says Professor Riley. ( AAP: Dan Peled )

Professors Ewing and Riley cite a lack of mentoring from more experienced teachers as one of the biggest problems affecting graduates.

"New teachers need support once they're in schools," Professor Ewing says. "A well-mentored new teacher is three times more likely to stay in the game."

But more experienced teachers often aren't willing to take on these additional mentoring roles; their workload is already beyond capacity.

With the advent of Professional Teaching Standards in 2011, all teachers — including those with extensive experience — were burdened with an additional administrative task designed to provide a framework for teacher professionalism and ongoing accreditation.

This means an experienced teacher's time is now spent documenting their own worth; there's no time left to support colleagues, new or old.

"This is our obsession with teacher accountability playing out," Professor Riley says.

"We've made it an adversarial profession, when it should be collegial. Teachers are competing for positions and constantly trying to make themselves look highly employable. What they should be focussed on is their students and their teaching."

It's not just 'new teachers' that are leaving, either

Research suggests many long-serving teachers are also retiring early, feeling utterly spent.

"And they mourn the loss," Professor Riley says.

"They miss the kids and they miss teaching — but the demands of the job simply become too much."

Like many of the new teachers who leave, these more experienced professionals are disillusioned.

There is ongoing pressure on teachers to improve test results, lift the profile of the profession, meet the teaching standards and deliver — faultlessly — an overcrowded curriculum.

"Experienced teachers have had enough," Professor Riley says.

And as they leave, they take with them their expertise and their ability to mentor and guide new and mid-career teachers.

It seems that consistent collection and analysis of data on teacher attrition — on a national scale — is urgently required.

The most comprehensive and recent information available is the federal government's National Teaching Workforce Dataset report published in 2014.

The data was collected in order to "provide understanding and insight into school teachers across Australia". However, the report itself acknowledges "limitations" in relation to "the completeness and accuracy of some data items".

"Teaching is a big workforce that nobody's monitoring," Professor Riley says. "And that impacts our ability to make plans for the future."

Without accurate and comprehensive data collection it cannot be determined how many teachers are seeking an alternate career, how many plan on returning to the workforce and how many retire early.

What's more, teacher shortages — already evident in remote and regional areas — seem likely to continue given the number of students is predicted to increase 26 per cent by 2022.

This, combined with the ageing workforce and high attrition rates, will likely result in larger class sizes, teachers teaching out of field and less experienced teachers being called upon to do more, all of which have serious implications for students and their learning.

So given what's at stake, why aren't we tracking attrition more closely?

"It's an issue of complexity and of cost," says Professor Riley.

"We simply don't have the sophisticated systems in place to record all the nuances associated with teachers as they leave and shift within the profession."

Of course, without that data, the size of the problem can never be fully understood and, more importantly, the reasons why teachers leave cannot be addressed.

"We aren't investing in our teachers," Professor Riley says.

"We still aren't resolving the problem."