It’s 12.30pm and there’s one lesson left before lunch. You’re teaching your favourite group of animated, engaged pupils, who you’re sure will relish the lesson on religious festivals you’ve painstakingly planned. But contrary to expectation, the pupils are not engaged. Not even the topic of self-flagellation elicits any hint of intrigue. They are more interested in the commotion outside involving a leaf blower.

If you’ve been in a similar situation yourself with a class - or even a staff meeting full of colleagues - you can take comfort in the fact that it is probably not down to your teaching or leadership skills. More likely, it is a case of decision fatigue, which results when our brain’s ability to process information becomes diminished following a period of sustained decision-making.

The execution of any act of volition, be it making a choice about where to sit, resisting the distractions around us or controlling our emotions, depletes the limited cognitive reserves upon which our mental processes draw. An understanding of decision fatigue is our best defence against its potential to undermine not only our lessons, but also the sessions that we deliver as leaders, such as CPD training or staff briefings.

So what do we need to know? Well, irrespective of our age or natural intelligence, studies have shown that decision fatigue inevitably leads to three possible outcomes:

* Reduced performance in further acts of related or unrelated volition. It has been shown that subjecting children aged between 6 and 13 to the “marshmallow test” - placing tempting snacks within easy reach and leaving them on their own under strict instruction not to pilfer any - causes their subsequent productivity in very simple tasks to decline significantly.

* Increased use of shortcuts when deciding how to behave. Car dealerships are known to set out their buyer customisation processes in an order that puts questions with the largest number of options first; this causes customers to tire cognitively earlier and to resort increasingly to default options - the ones with the greatest profit margin for the dealership.

* Avoidance of further decisions. When asked to imagine that they possess a surplus £10,000 and have the opportunity to invest it in a venture with average risk but above-average return, most “mentally fresh” people jump at the chance. On the other hand, those who have previously been subjected to cognitive exertion tend to leave the money where it is.

Bearing these studies in mind, it is little wonder that both teachers and pupils become mentally fatigued when faced with lesson after lesson, each of which involves countless choices and the need to resist an endless array of competing demands on our attention. The result of that fatigue is lethargy, distraction and, at times, astonishing indecision.

Maintaining adequate glucose levels and getting sufficient rest are the physiological keys to minimising and recovering from decision fatigue, but in most cases these are outside of our control as teachers and leaders. So the best option is for us to plan our lessons and staff sessions with decision fatigue in mind. This means that challenging material should, as far as possible, be delivered at the start of a day or immediately after morning breaks or lunchtimes, when pupils are relatively rested and riding glucose highs from having just eaten.

Equally, exercises that require real participation and engagement should take place early in lessons. Introducing your pupils to the topic of a lesson through easy activities that gradually build to an examination-standard finale is likely to be counterproductive, as is making them complete a challenging past paper during a pre-lunch double lesson.

Group work also needs careful thought. Collaboration is undoubtedly a powerful tool in facilitating mutual challenge and support, but it’s equally a source of distraction, so it should be scheduled for periods in which pupils have sufficient cognitive reserves to take the most from it.

Keeping colleagues perky

All of these points will hold just as true when you are working with colleagues, so they should be taken into account, for example, when planning an Inset day.

We should ask ourselves whether the nature of the tasks we set, and the environments in which we set them, should be reconsidered in light of decision fatigue. Which cognitive exertions are we asking of our pupils or colleagues? Are all of the decisions we are asking them to make constructive for their learning or are they making choices that are inconsequential, but still mentally draining? Are our classrooms minimally distracting and emotionally neutral or are they inadvertently subjecting pupils to unnecessary exertion?

Only by accounting for our pupils’ - and our own - cognitive constraints can we hope to fully facilitate effective learning.

Graham Mallard is head of academic enrichment and research, and head of economics and business at Cheltenham College