When knowledge is wrong…

Babies are born knowing physics. They express surprise when an object appears to be suspended in mid-air or pass through walls (nice article here). These are the primitive physics schemas we are all born with. Onto these, we add experiences from our lives: metals are cold; batteries run out of charge; the sun moves. Then in physics lessons we try to supplant this knowledge with formalised knowledge. With mixed results.


A metal cup to keep drinks cold.

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What are the Cognitive Loads of reading and how can we reduce them?

Reading is a physics problem that doesn’t receive much attention in class. I think it should. Science professionals read a lot:


How many hours of professional STEM reading per week?


It turns out that the people who responded to the survey read a lot. Almost 85% of them read professional texts for more than 5 hours per week and 20% of them read for more than 15 hours per week. And they read to learn…


Why STEM professionals read

But most weren’t taught to do it at school. 


Who teaches scientists and engineers to read professional texts?

This last chart troubles me. I know STEM texts (exams, textbooks, papers) are different to other texts. They use different vocabulary; follow different conventions and have a different purpose. Either learning to read these texts is so easy, it doesn’t require teaching, or it is hard and we are letting learners down.

How many capable young scientists and engineers are dropping out because they can’t access the information in texts? I worry about this a lot.

Cognitive Load Theory explains why reading is difficult and tells us how to make it easier. All three memories are in use:

  • long-term memory – the knowledge you already have. Commit as much to memory as possible – use quizzes every lesson. 
  • working memory – where we compare what we’ve read to what we know and try to make meaning. There isn’t much we can do to boost this, though a good night’s sleep always helps me. 
  • external memory – the text, and any scribbles you’ve added to it. This is a skill and we should teach it. 

Comprehension depends most on what you already know. The two most important things for reading are in your long term memory (or they need to be). They are vocabulary and knowledge. Readers who are equipped with these are equipped to understand texts.


Science teachers are good at teaching science vocabulary. We explain clearly; we use example sentences; we revisit; we match words to diagrams. We use every trick we know.

But we ignore key non-specialist vocabulary. Words like: determine, suggest, establish and  system (I took these from a couple of recent GCSE papers).

These words should be taken as seriously as technical vocabulary. It is hard to choose words to focus on. I tend to teach words as I come across them in textbooks and exam papers (especially if I think they could come up again).


Along with vocabulary, the most important part of understanding is what you already know: your schemata. As we read, the information in the text is held in your working memory to be presented to knowledge from your long-term memory like a debutante or a novice speed-dater. If sense can be made, great. If not, the reader has work to do. 


Skills get tough press – but there are a few reading skills (or habits) which make a difference. These are the four that expert science readers (like us) use most often.


  • I Wonder…. Expert readers ask questions of the text. Often these questions are related to meaning, but they can be “I wonder what that word means?” or, “I wonder why the writer said that…”
  • In other words…. Paraphrasing (rewording, often making clearer) is a powerful comprehension checking skill/habit.
  • I predict…. Asking readers to predict what comes next in a test is a useful way of drawing attention to the structure and conventions of scientific texts – it is extremely useful when scanning a text for the information you want to be able to predict whether the information might be in a nearby section.
  • So far… Summarising is a habit which encourages prioritisation of information.


If these activities can be practiced enough (several times over a few weeks, with occasional top-ups) they quickly become part of a reader’s reading schema, increasing your students’ ability to learn from texts.

This blog is a development of the blog I wrote in 2015 for the Royal Society of Chemistry – here. I am reassured to find that I still agree with most of what I wrote then. Thank you if you’ve stuck with me all this time!


Ratio, Load and Difficulty – 3 Lesson Sliders

ratioloaddifficulty v3

In my mental lesson control booth, I have three sliders I try to get right.


The first slider is ratio. I learnt this idea from Teach Like a Champion by @Doug_Lemov, who got it from Dave Levin from Kipp.

Ratio is the amount individual students spend actively thinking in class compared to the total lesson time. For example, in a teacher-to-one Q+A session, the ratio is low for every child who isn’t asked the question – most children don’t think much in those circumstances. You can increase the ratio by asking a question to the class and then getting them to answer it in pairs.

I used to worry that increasing ratio meant that direct instruction and teacher- modelling were low ratio. But pushing the ratio slider up a little in these activities means the teacher says what she needs to say as clearly and succinctly as possible, before the learners get active. That’s a good thing.


By load, I mean cognitive load. I want to bring this as low as I can so that my students are thinking about the thing I want them to learn. I reduce all of the extraneous ‘noise’ – especially for novices.

This week I have been working on direct speech with my class. There are many loads on a novice with writing direct speech: paragraphs, capital letters, commas, question marks, inside the speech marks or out. Added to that, they wanted to write their own dialogue.

I pulled the load slider as low as I could – we used goal free to look at speech from a book. They wrote their dialogues as playscripts first before converting to direct speech. Each element was difficult, but I reduced the load.


When I first learnt about cognitive load, I thought it meant make the thinking easy. It doesn’t. Cognitive load theory simply says take out the extraneous thinking – the undesirable difficulties and make the thinking about the thing you want to achieve. And that thing can (and should) be difficult.

There is an optimum difficulty for tasks – Bjorn calls them desirable difficulties (see here). He makes a terribly important point – one that I missed for many years – performing well in class is not the same as learning well. The struggle is important.

So whenever you can:

  1. turn up the ratio
  2. turn down the load
  3. set the difficulty to desirable.


My experience with ‘goal-free’ – a Cognitive Load Theory strategy

@Olivercaviglioli ‘s wonderful document on Cognitive Load Theory here introduced me to the “Goal-Free Effect” – a Cognitive Load Theory (CLT) strategy that I was unfamiliar with. Goal-Free was the first CLT strategy – that’s what comes of learning your theories from blogs.

The strategy reduces cognitive load by removing the actual question from the problem, leaving just infromation, often in the form of a diagram.

This is how I’ve been using it to help my pupils prepare for the maths reasoning papers in the SATs.


Goal-Free KS2 Maths Reasoning Question

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The single most important thing for teachers to know… Version 2

WIliam CLT

Dear Reader,

Yesterday I published a post on Cognitive Load Theory (here) and how I use it in class. I was concerned that although I had been careful in my reading, I was sure to have “invented” modifications of my own (also known as “mistakes”). Sure enough, several readers kindly (and gently) pointed out where I had been creative/careless/wrong. My thanks especially to  ,  for his great essay here and @FurtherEdagogy.

This is version two of my post.

Please continue to comment – and never assume I am an expert.



Cognitive Load Theory, and How to Use It 2.0

Here is my explanation for how Cognitive Load Theory works and how to use it.

CLT schematic (3)

The elements of Cognitive Load Theory – long-term memory, working memory and external memory.

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The single most important thing for teachers to know…

WIliam CLT

Dear Reader,

There is a lot being written about Cognitive Load Theory (CLT) and how important it is. I have written this blog to share my understanding – please send me corrections, recommendations and advice.

My own understanding has been developed through:

  • Hattie’s ‘The Science of How We Learn”
  • Willingham’s “Why Students Hate School”
  • Kellog’s “The Psychology of Writing”
  • Oliver Caviglioli’s summary of Sweller’s “Cognitive Load Theory”

My aim it to add something useful for teachers. I am a teacher, not a psychologist. Please send me corrections and recommendations so that I can improve this post.

Thank you for taking the time to read it. I hope it is useful.


Cognitive Load Theory, and How to Use It

Here is my explanation for how cognitive load theory works and how to use it.

CLT schematic (2)

A Model Of Cognitive Load Theory

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