Not long ago, I went to see a documentary about a man who had climbed one of the most technically difficult rock faces in the world, and done it "free solo" – with no ropes or safety equipment. One mistake and he would certainly be dead; impressive, though I’d like to see him teach 9D last thing on a Friday.

One question resounded through the film: what had possessed him to say yes to this challenge? In fact, the answer was more subtle. He’d felt able to accept it because he was very clear about what he said no to. His apparently boundless feat was made possible because of the firm boundaries he set around himself.

In one of the key scenes in the film, he begins his free-solo ascent of El Capitan in Yosemite National Park, but — after 600 feet or so — decides to pull back and stop. Why? Because he felt that the cameras around him were affecting his judgement. He didn’t want to be saying yes to this potentially perilous task simply because he was under observation. Sound familiar?

Setting boundaries

When was the last time you said no? My experience of teaching in different London schools over the past 20 years has been that so much of what we do relies not just on the goodwill of teachers, but on their natural will to please, their reflex to be obedient to authority structures.

Think back — what kind of student were you at school? Most teachers I have asked this question to admit to having been "good" students, the ones who won’t complain when you set extra homework, who will stay behind and put the textbooks away, who offer no resistance because they believe that their teachers are unimpeachable.

My worry is that this laudable unquestioning enthusiasm and trust that "the system knows best" can make for a dysfunctional staffroom, one where people whisper amongst themselves about the intolerable pressures of rising workload, but have no clear boundaries about when they need to say no to new demands that school leaders make. Why? Partly because – like the climber in the film – they feel the weight of constant observation, the ever-present "what if an inspector calls…?" That, while unspoken, rings loud through each new diktat. 

Cutting corners or trimming the fat?

I recently heard a story about a colleague in another school who had just been given notice of inspection. An email came round demanding that all staff must complete lesson plans for all of their lessons during the inspection period, using a four-page template that was attached. When questioned about this, pointing out Ofsted’s own "myth-buster" page that makes it clear that inspectors didn’t need individual lesson plans, the reply came that that didn’t matter, and that it would look better for the school if it were done anyway.

The colleague took her chances and produced half-page context sheets in case she was visited. Others slaved deep into the early hours dutifully following instructions, knowing deep down that this was nonsense, but unable to risk letting the school down. Only afterwards, as the hundreds of hours of work were shown to be a waste, did anger about this find voice.

It can be hard to say no in teaching because we are dealing with children. While this remains a job, not a religious vocation, we are doing more than manufacturing widgets. Yet in many cases – these lesson plans, for example – the extra demands are not focused on delivering more for our students. So much extra workload is about producing evidence for those we are not actually teaching. This can smack of a lack of trust in our professionalism, an anxiety among school leaders about what is going on in rooms they cannot see.

Use your own judgement

In my role as a union rep (and staffroom old lag), my advice to colleagues is to do three things when any new demand is made. Firstly, ask yourself if you have the resources to meet it. If you don’t, you should then calmly request that your manager either take some other demand away, extend the deadline, or reconsider it entirely, reflecting on whether it is focused on benefiting students.

With three-quarters of teachers saying that increasing workload is having a serious impact on their physical and mental health, with panic attacks, tears, anxiety and breakdown sadly too common across the nation’s staffrooms, having the courage to own your professional judgement can be hugely liberating.

Even if you began as an NQT this September, you already have hundreds of hours of classroom experience. You are very probably a university graduate with focused postgraduate training. If you are not yet an expert in your field, you are fast becoming so. Though you work with children, you are not a child. You know your job and the students in your care.

Most importantly, you know your limits. The climber in the film is still alive because he knew when to say no. With so many teachers "falling off the mountain", it’s clear that our long-term survival in the profession depends on our ability to make smart calls, to politely decline when asked to add one more thing because we who live at the rock face each and every day must be trusted to know where our breaking point is.

Kester Brewin teaches maths in south-east London. While working as a teacher, he has been a consultant for BBC Education, and is the author of a number of books on culture and religion. He tweets @kesterbrewin