The 3 most important things to understand about the most important thing for you to know.

I want you dear reader, especially if you are over 25, to do me a favour.  I want you to look back over your own school education or even your university or college education and bring to mind your best teacher.  Not necessarily your favourite teacher, but the one who you now realise had a particular gift for helping you learn.  Have you got them?  Can you remember them in the classroom?  They almost certainly had never heard of Cognitive Load theory.  They were possibly a brilliant teacher and they had never heard of what Dylan Wiliam described as the single most important thing all teachers should know about.  (if you are under 25 there is a possibility that they might have.) Cognitive Load is the idea that every task we ask students to complete has a certain demand.  Students ability to tackle this activity depends on factors such as the strength of their working memory, what knowledge they already have and the manner that the task is presented.

Does this mean that cognitive load is therefore not important, no.  They almost certainly had learned through experience, or through reflection on their practice exactly how to ensure that tasks were presented in such a way that you as student could access them easily.  Is Cognitive Load a new thing? As a term yes but not as a principle.

Twenty six years ago I visited a secondary school in Cambridge where I was trying to finish off a research project into Down’s syndrome.  I was contemplating coming into teaching and just wanted to visit a school to see what it was like.  Parkside School was where some friend’s children went and they reported it was ok, so I phoned up.  I was lucky enough to meet Elaine Wilson, the Head of science there, who was an inspirational teacher and would go on to be Salter’s Chemistry teacher of the year before finding her way into academia in Cambridge University.  I clearly remember a conversation regarding a lesson I observed where she was using a number of demonstrations to discuss particles and their characteristics.  I had seen another of her colleagues perform a similar lesson and asked Elaine why she didn’t use a particular practical I had seen earlier.  Her colleague had got the students to set up the classic starch solution inside a piece of visking tubing with iodine outside and watching over the remainder of the lesson the iodine diffuse into the tube which turns blue.


Elaine’s explanation was that she had stopped doing this experiment because the instructions and setting up was too complicated.  The students missed the diffusion, getting lost in the pipetting, knot tying and other instructions.  Her simple explanation then was “The Signal to noise ratio wasn’t high enough.” The signal; diffusion, got lost in the noise; setting up the experiment.  This is Cognitive load by any other name.  Did Elaine call it this? Of course not.

If cognitive load is the most important thing for teachers to understand, then the most important thing for teachers to understand about cognitive load is that it cannot be measured.  Why is this important? On a scientific basis it means that it is difficult to study.  Without quantitative data it becomes hard to determine what it’s effect in the classroom and on learning truly is.  There are a number of critiques of cognitive load that go into more detail (see the further reading at the end)  and lack of a quantitative response is not the only critique.  The other reason is practical.  The cognitive load of an activity varies from lesson to lesson, from class to class and from pupil to pupil.  All we can do as teachers is consider the relative cognitive load.  We can aim to reduce (or sometimes raise) the load but we can’t say by how much.

I like the simplified model for thinking about cognitive load from Reif’s Cognitive Science in the classroom and explained well in his blog by Adam Boxer.  For the more mathematical among us it also enables us to visualize the effect of our behaviours.

cog load simple

Reif simplifies all the extraneous, intrinsic germane bit into one simple formula:


Those of you with enough maths skills will immediately see the significance of this.  As Adam Boxer says in his excellent blog post on the subject:

“When presenting students with a formula like this, we would explain that increasing “task demand” increases load, whereas increasing “available resources” decreases load. Load, resources and demand are variables: they are things that can change, or be kept the same. This is important because there are some things that might be out of our control, and if that is the case we must manipulate the other variables to compensate.”

The demand of an activity might be beyond our control.  We have to teach ionic bonding, genetic inheritance, kinetic energy (insert tricky topics from your own subject) as they are on the chosen exam specification.  But the resources that are available might be in our control.

The available resources a student has to tackle the cognitive load of an activity comprise of two parts.  The things they bring to the lesson and the things we as the teacher provide.  They bring their prior knowledge of the topic, their engagement in the activity, their working memory (there are also concerns with working memory as a thing, this will form a later post).  You bring the modelling demonstration, the list of key words, simplified explanation, the scaffolding document etc etc.

This is where the fun starts.  As we all know things like prior knowledge, engagement and working memory are variables.  They change from pupil to pupil and they change from day to day. A student who is tired, a student who is hungry, a student who has just been “counselled loudly” by their head of year will have different levels of these three variables to their normal state.  Your carefully crafted activity where you have worked hard to provide the necessary available resources can come crashing down around your ears.  One, two, several or in the worst case, a class full of students just don’t get it. Is this a failure of cognitive load, of course not.  Have you wasted your time? Probably not because the cruel irony of teaching is that the same activity on another day with the same class will possibly work just fine.  So I would say the second most important thing for teachers to know about cognitive load is to just do your best.  Work to manage the cognitive load of your activities but in the end you just have to suck it and see.

The final point and the third thing for you to know about cognitive load is that sometimes you will need to increase it!!! Breaking down a task into smaller and smaller pieces for some might make it too easy, students will not be challenged and could get bored.  Deepening understanding, helping some students learn, providing able students with challenge can all be assisted by increasing the task demand.  This could be as simple as removing the scaffolding earlier, it could be by reducing the time available for the task or giving the student more parts of the activity to do at once.  An example of the latter would be say in an activity to complete multi-step calculations (eg titrations.)  For some students you might go through each stage (balance equation, number of moles of the known solution, the ratio of known to unknown, the number of moles of the unknown, the concentration of the unknown) for others you might lump some of these together. To use an example from English as quoted by Adam Boxer

In English for example, you might want students to be able to answer the question “How is Slim presented in this extract?” and break it down into 1) find a quotation that shows Slim being presented as empathetic, 2) analyse the methods the writer has used to show that he is empathetic, and so on for other characteristics (3).

To increase the load you could just ask the question; How is Slim presented?

Who am I to disagree with Dylan Wiliam.  Cognitive load is important.  If you have been teaching a while you will most likely be already using strategies to reduce cognitive load in your current practice.  If you are starting out in your thinking on this topic it can be easy to get drawn into creating lengthy strategies to reduce cognitive load.  Just do your best and be prepared to change.

Further reading on cognitive load.

It has been refreshing to read a number of criticism of cognitive load theory:

A blog post by Doug Houton from the early days of CLT.

This contains links to further articles

And a balanced article on it from the Chartered College of teachings Impact Magazine

For some classics on Cognitive Load see one of Sweller’s original papers

The original work by Reif is this one

Reif F (2010) Applying Cognitive Science to Education. Thinking and Learning in Scientific and Other Complex Domains. Cambridge, MA: The MIT Press.  As you can see this is a book and so cannot be accessed on line, so it is more of a challenge to get hold of.  I am relying on quotations from other author’s until my copy arrives (mae culpa.)

Adam Boxer’s reading list is a page I am likely to refer to regularly it can be found here

One reference that resonated with this article was this one


PS I have tried to use royalty free images throughout this blog;  if am mistaken and you are the owner of an image please get in touch.


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