Dual-coding in Science

Dual-coding is a very effective tool in teaching when used correctly. For me, the use of an academically rigorous piece of writing supported by a simple but clear image has a powerful impact on pupil learning. Equally, a verbal explanation to go along with a simple image has huge merit. I don’t claim to be an expert in this – I have just done some very basic reading, and have attempted to apply ideas in the classroom and it seems to be working. So, here goes…

Below, I give a very stark example where class understanding literally flipped from nearly no-one to nearly everyone, after I used a diagram + explanation, and read a text. Later in this post, I consider the principles of using dual-coding effectively in science, and I give some other examples including: concepts, experiments, decision trees, processes & mind maps. Of course, I imagine this can be transferred to other subjects, but my examples are all from science.


A recent example I can share involved teaching my Y10s about the uses of glucose by plants. Here is an extract from a piece of writing which we read together as a class:

‘Plants can use glucose in another polymerisation reaction to make starch. This glucose polymer is used for storing excess glucose, much in the same way as humans store excess glucose as glycogen in the muscles and liver. Why can’t plants simply store glucose? Glucose is soluble in water. This means that it will make the solution in a cell more concentrated, and result in osmosis happening. Since plants are constantly making glucose during the day, the concentration of the solutions in the cells would get higher and higher. This would mean more and more water would move into the plant cells by osmosis – the plant would not be able to control how much water was inside its cells. To solve this problem, plants polymerise glucose into starch, which is insoluble. Starch does not affect the osmotic (water) balance of the cell. This means that plants can store large amounts of starch in their cells.’

I checked if pupils knew what ‘soluble’, ‘polymerisation’ and ‘osmosis’ meant, and since they were concepts we had done many times before, there were no issues. However, when I asked which pupils felt confident enough to summarise what this paragraph was saying, only one hand in the class went up. I must admit, this took me by surprise. The ‘curse of knowledge’ I have, as it is called, meant that what seemed blindingly straight-forward to me, had in fact, baffled my pupils. [Note, I do use such self-reporting – asking pupils if they understand – because this is class who I know are very honest about their understanding. This doesn’t mean that I don’t ask them when they claim they do understand. Always ask them to prove they understand by getting them to explain.]

So I turned to my ever-trusted whiteboard and marker, and started drawing on the board. Once I had finished, I asked the same question again: ‘Who thinks they can now explain what the paragraph is saying?’. To my surprise, ALL but one or two hands went up in the class! This lesson was full of surprises! The power of dual-coding became apparent. Here is the image I drew up on the board:

Screen shot 2017-05-13 at 14.22.20

In real time, as I drew more glucose molecules in the first cell, I asked whether the solution inside was becoming more or less concentrated, and asked what effect this would have. Water would move in by osmosis, of course! If this kept happening, what would happen to the cell? Then, I drew the second cell and polymerised the glucose by drawing bonds between them and asked if this was soluble or insoluble. Would the osmotic balance be affected? Why not?

Critics might argue that I could have drawn the image and not had the ‘confusing’ text at the start, which seemed to hinder rather than help understanding this concept. But here’s where I found why both text and image are essential: the pupils were using the text to use more academic language. Had I not written the paragraph with phrases such as ‘polymerisation’ and ‘osmotic balance’, the pupils would not have been able to use the vocabulary as well.

The knowledge that this is a polymerisation reaction is not on the GCSE specification in this section, so I could have omitted it. But I chose not to. I  want my pupils to use as much academic vocabulary as possible. I want to model excellent scientific writing so that they can encode this language. An image and verbal explanation alone may not have achieved this. We tend to talk less academically than when we write, especially if we are conscious of writing rigorously and including vocabulary that goes beyond what is expected.

Principles of dual-coding

  1. Keep the diagram very simple, focussing only the elements important to the explanation. This avoids distractions that result in cognitive overload.
  2. Avoid sacrificing accuracy for clarity where relevant. For example, I draw arrows going both ways in the osmosis example, with a bigger arrow into the first cell to show that osmosis is net movement of water. This helps prevent the common misconception that water only moves in from a dilute to a concentrated solution.
  3. Text/verbal information must complement the image.
  4. Ask yourself if an image is necessary. I could have used an image of a leaf, a diagram of a glucose molecule, an image of a cell bursting… but all of these are unnecessary. Students know what leaf looks like, don’t need to know the molecular structure of glucose to understand the point I am making and can imagine a cell bursting.
  5. Ask questions throughout to check for understanding.

Other examples

Later that lesson we studied making inferences in science. Here is the text we looked at:

Q: If there are two plants, and one plant’s leaves contain a lot of starch, whilst the other plant’s leaves do not, what would that tell you about the two plants?

A: The presence of starch in a plant indicates photosynthesis has taken place. This means we can use the presence of starch to infer whether or not a plant has been photosynthesising.

Inferences are very important in science, because we cannot always observe phenomena directly. When this is the case we use the powerful idea of cause and effect. We can assume that the observation we are making (the effect we see) must have had a cause. In this case, when we notice one plant has starch, we can safely infer that the starch was made because the plant was photosynthesising. This assumption is valid because we know that photosynthesis produces glucose, which is used to make starch. It is very unlikely that the starch appeared in the plant for any other reason. Equally, we can infer that the other plant did not photosynthesise and so did not make any starch. These are valid inferences, because the likelihood they are true is very high.

Of course, there is a danger when scientists make inferences that they do not account for other possible causes. For example, a scientist might infer that the plant without starch did not photosynthesise because it did not have enough water. However, this might be untrue, because the plant may have had plenty of water. Rather, there could have been another limiting factor for photosynthesis such as a lack of light, which could also explain why the plant did not photosynthesise. Such an inference is not a valid one. To be sure, we must collect more data.

Here, a very simple diagram I used helped my pupils to grasp this.

Screen shot 2017-05-13 at 14.22.45

Again, lots of simple questioning revealed that this image helped clarify what I meant by an ‘inference’ in science, as well as helping to make ‘valid’ and ‘invalid’ inferences distinct.


Some experiments are fiendishly difficult to understand. My class found one of the GCSE required practicals, where an insoluble base is added in excess to a soluble acid to make a pure salt, particularly challenging.  The concepts to get clear were:

  1. Why should the base be insoluble?
  2. Why should it be added in excess?
  3. Why is filtration required before crystallisation?
  4. Why are only these two separation processes needed to obtain a pure salt?

I realised that successfully understanding this practical boiled down to being clear exactly what was in the beaker at each step. So I drew this diagram to help make this clear:

Screen shot 2017-05-13 at 14.37.07

  1. Start with dilute sulphuric acid in the beaker. The image helps clarify to pupils that this means there is both water and sulphuric acid in the beaker.
  2. Adding a small amount of copper oxide causes it to react fully with the acid. This results in there being less acid (one of the reactants, currently in excess), no copper oxide (limiting reactant), more water (a product) and the appearance of a new product: copper sulphate. That there is no copper oxide, is made clear by the image.
  3. Add base to excess. There is now no more sulphuric acid (limiting reactant) since it has reacted fully. *This is key to understand – and the image was invaluable to get this across.* There are only three substances in the beaker now. There is spare copper oxide left over and since it is insoluble it is solid, and the two products of the reaction.
  4. We want to isolate only one of these: the copper sulphate. Since copper oxide is solid, it can be separated using filtration.
  5. Since copper sulphate is soluble, and it is currently dissolved in water, the water can be evaporated to leave pure copper sulphate crystals.

Decision trees

Another invaluable use of images is decision trees, such as this one I made for electrolysis:

Screen shot 2017-05-13 at 14.43.29 This summarises the ideas in a logical way, helping pupils to remember.


Processes lend themselves to diagrams, but simplifying them is the trick. It took teaching this topic several times for me to find a simple diagram to use. Hormones controlling the menstrual cycle:

Screen shot 2017-05-13 at 14.54.17

Mind maps

For summarising information, I use mind maps. I use them in three main ways:

  1. I give a lecture, where pupils follow and annotate the mind map. This is good for teaching a new topic.
  2. I give pupils a mind map and ask them to turn it into a paragraph. This helps pupils practice articulating and sequencing ideas. It really helps them make links.
  3. If pupils are confident on a topic, I get them to make their own. It is a good way for them to make links. Sometimes, I use a checklist of information they must include in a mind map, forcing them to make links.

Screen shot 2017-05-13 at 14.52.32

Hope this is useful. It would be great to hear what you have tried, and feedback on what I have done so far is welcome.



21 thoughts on “Dual-coding in Science

  1. This is so useful- thanks for writing and sharing. Do you and your dept collaborate to plan for these images, or do you do them more or less spontaneously in the class ?


  2. Thanks for these; as I commented on Twitter, I found the post a great guide to applying the principles of dual-coding in science. I think at the time I used the words simple and clear, but I think straight-forward is better than simple.

    I like the idea of having students convert text into diagrams and vice versa; I sometimes advocate providing different summary tables so students must look for different aspects of a situation. Providing particular phrases and terms in the text is a great way for us to model what we see as correct language. They could also use a good paragraph to improve a provided graphic that lacks technical terms, getting them used to the idea of ‘translating’ between everyday English and precise vocabulary.

    I think often in science we use diagrams and text alongside without adequate reflection or planning. I found your comments alongside the photosynthesis example very useful – there are many we could use (and sometimes would) but some are clearly more useful than others. As we tell the kids when they produce revision materials, illustrations or pretty colours are a waste of time unless they add meaning. I used to give two example mind-maps, both based on student work, for them to compare. One had a hundred colours of lines and underlining, cloud-shapes around some words and others in bubble-writing. The other used three colours, highlighting positives (green), negatives (red) and definitions (blue). Arguably, only the second was dual-coded – the other was simply decorative!

    Flow charts are something you’ve not mentioned above, but are an obvious addition when dealing with any processes. The rock and water cycles are probably the first two students encounter, and considering arrows as processes (which have technical descriptions, and can happen quickly or slowly) show where the cycles get ‘stalled’. In physics, we are currently facing a lot of issues in how Sankey diagrams are less helpful with the ‘new’ energy language. As long as the arrows are scaled to the power of each pathway, they work well. It remains to be seen how well this will work in biological contexts!

    I will be thinking about these ideas some more – thank you for getting me started.


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  5. Hello Bunsen Blue! Thank you so much – we will be looking at our copper sulfate crystals on Monday so I plan to ask the students to label beaker diagrams with what chemicals or ions they think are in there at each stage… this should be a good way to push home the idea that it contains water – often forgotten as part of a solution!

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