Back in the 2000s, “thinking hats” were a mega-cool concept in schools. Available in six different colours, each one signified a way of thinking about a problem. For example, yellow-hat thinking involved looking positively at a problem, while people wearing white hats were told to look purely at facts.

The concept is less cool these days. Rarely does one enter a primary school to find a multi-coloured set of trilbies sitting on the teacher’s desk. But the approach can still be helpful when others are gung-ho for a solution which you feel needs more evaluation.

Flexible working is a flavour-of-the-month idea for improving teacher workload and lessening turnover. White-hat thinking shows it’s needed: teachers are leaving at higher rates and fewer people are entering, right as a demographic bulge of teenagers maraud into schools.

From a yellow-hat perspective, flexible working would enable more people to fit a job that can seem brutally inflexible around their complicated personal lives.

But there are also the red hat of hunches and the black hat of cautions, and these are where my fears start to creep in.

Promoting flexible working doesn’t always resolve teacher shortages. It can actually make them worse.

We may go from a situation of losing one teacher, to losing half the time of four teachers

Let’s imagine a teacher who will leave the profession unless they can go part-time. By being flexible, they may stay. This is good. But there will also be teachers who are NOT currently thinking of leaving who also decide part-time sounds like a good idea and will reduce their hours.

So we may go from a situation of losing one teacher, to losing half the time of four teachers. Instead of needing to replace one teacher, we now need to replace two.

This is what happened with GPs in the early 2000s. The job was changed to be more flexible and promoted as “family-friendly” in order to attract more people. It worked, but over time the average number of hours worked by GPs fell, and the shortage is now worse.

Secondly, flexible working approaches can counterintuitively end up meaning people work more than before. As companies like Netflix and Virgin moved to unlimited holiday policies, evidence has shown that workers actually take fewer days, but don’t have the benefit of being paid back at the end of the year for untaken leave days.

In Germany, organisations that moved to flexible working saw hours rise among staff. Notably, however, men tend to get paid more for this, largely because the assumption is that extra hours undertaken will be paid overtime. Not so for teachers in the UK, sadly.

All of which leads to my third concern. Having written about this issue earlier this week I was contacted by many people saying they’d chosen to go part-time so they could catch up with lesson-planning and marking on their “off” days in return for seeing their children or doing a hobby on the weekend.

For teachers who can drop to four days of pay, that’s great, but what does it mean for teachers who need a five-day income, especially younger ones with huge debts and sky-high rents? Should they simply be expected to always work weekends for free to catch up?

Flexible working approaches can counterintuitively end up meaning people work more than before

The green thinking hat is for creative solutions: is there one?

At heart, teachers are contracted to work 1,265 hours of directed time per year. That is, for 1,265 hours, school leaders can tell teachers exactly where to be: teaching classes, attending meetings and so on. Beyond that, however, teachers must work “such reasonable additional hours as may be necessary to enable the effective discharge of the teacher’s professional duties”. But what counts as reasonable? In a system demanding excellence from everyone everywhere, the list is never-ending.

In the 1990s, when the deal was originally struck, teachers mainly spent their time outside of classes marking and, once a year, writing reports. Excel barely existed. Neither did PowerPoint. No emails. No mobile phones. Although work sometimes crept into personal life, it was more manageable.

At that time the 1,265 deal probably seemed like a coup. You could leave school when your allocated hours were done and mark in the comfort of your own home with few demands on how long you ought to do it, and no need to upload the results into a cloud so managers could check on you.

Now, in the modern era, that deal no longer works. Like the dreaded hats, it’s getting old.

It is now time we donned the blue hat pulled together all the findings, and created a new deal for teachers on working hours. There has to be a better way.

Laura McInerney is contributing editor of Schools Week