Making the juice worth the squeeze: The anatomy of lethal mutations

Early on in my Head of Science career I spent a whole year with an action plan built around growth mindset theory. Although I spent a long time campaigning for my school to adopt it and not make it a series of posters about ‘FAIL = First Attempt At Learning’ and categorising thoughts as being fixed or growth I fell into the same trap. I had a poster campaign that asked students “Are you a Yeti? Ask your science teacher.” and I used the yeti from the popular mobile game Plants Vs Zombies in my marketing, for some reason.


So I start this blog not from a place of smug superiority, but a place of curiosity. How do we end up with the ideas that make their way into the teaching profession taking on a mind of their own and changing so much from their original intent? Why can’t we seem to avoid taking good simple ideas and turning them into slightly less good, much more complicated ideas?

Why should I care about what other teachers do?

Time is the number one resource a teacher has. The education system itself is a giant operation in effective time management. I want teachers to have a good understanding of these concepts so they can make an informed choice about what they spend their time on. If I can help illuminate the mechanism that causes these changes it might possibly help us break the cycle. There is no doubt that there is more than one way to help students learn more in lessons and each teacher filters all the evidence and approaches they come across through their own ideology. However, I think the profession would benefit from greater clarity on what the evidence actually shows and what are different people’s personal choices in how that technique is used. 

What is a lethal mutation then?

“In education, the term ‘lethal mutation’ can sometimes be used to describe the phenomenon of perfectly sensible approaches to teaching being misunderstood or misapplied, to the point that they become harmful to students’ outcomes.”

D.Didau Teachwire

The key component here is the shifting of the consensus understanding moves away from the important features and fixates on certain aspects, often things that appeal to the teachers own values or aesthetic tastes. These aspects become the common features that less experienced teachers identify and then amplify. Unlike a genetic mutation, whereby one deletion or substitution can cause the entire gene to become faulty, lethal mutations are not an instantaneous process but a gradual frame shift of community understanding. They do appear to suffer from the danger of exponential growth though. As awareness of the technique increases as does the speed that the mutant variants replace the original idea within the community.

There might be research that has studied this in detail. I have tried my best to find it but have so far been unable to find a mechanism for how this arises. So I have taken a stab at it myself and would like to propose the following mechanism for how an educational technique might undergo a lethal mutation by accident, as a result of good natured, hard working teachers trying to help each other out. It’s a little clunky but it’s a starting point for now. My hope is by containing as much information as possible I can receive feedback and insight from other that help refine it. 

My proposed model for lethal mutations.

Essentially I think we have four stages.

Stage one, The green stage in the diagram above is the exposure and enamouring stage. This is when a teacher is exposed to a new technique. This facilitates them to go searching for examples. Crucially they are attracted to the examples which they find most appealing, either aesthetically or because a certain approach fits with their beliefs about what teaching should be. For example if you enjoy the minimalism of the noun project icons used in some dual coding examples you might prefer those examples, or if you think students are engaged by choice then you might prefer retrieval games instead of quizzes. If you think everything should have a dad joke or pun in it then you might plaster your walls with flipping yetis. *shakes head with embarrassment*

Stage two is the creating stage, purple in the diagram. This is when the teacher puts in discretionary effort to produce or adapt resources that appeal to them. Crucially this often results with a misunderstanding of the underlying principle or a selection bias due to their educational values. Why teachers might misunderstand the technique is varied but often easily put down to being short on time and so engaging with things at a surface level. A good example here is thinking retrieval practice is about getting students to answer questions on prior work. In fact retrieval is the idea of getting students to try and think back and retrieve knowledge from their long term memory. While these two ideas are identical on the surface the second has ramifications on how students should work, what prompts that should be given etc.. which lead to the process having a greater success rate. 

Stage three has two possible mechanisms. One local, one online.

3a is the peer status selection, the orange stage. In this stage these new resources increase the teachers status within their own school. They become the ‘metacognition person’ or the ‘instructional coaching person’ this creates an incentive to expand their work within the new area. To the hammer everything is a nail and in a similar vein the teacher looks at all problems through this new technique they are now well known for. They stop doing some other things that are beneficial to students to focus on spending more time on their new pet technique. More crucially the adaptive agents that teachers are mean that other staff see this change in status and change their practice to align with it. This might lead to devaluing other versions of the same technique or lead to a monoculture which stifles innovation within the school. 

Alternatively they can go to stage 3b, called peer proliferation. This is the blue stage in the diagram. This outlines the role those of us that share our work on social media have on the system. We publicise our work on blogs, tweets and even books creating a network of weak ties. Here our interpretation of the technique gets magnified and legitimised. Other teachers run the risk of contributing to the lethal mutation by either correctly applying our misinterpretation or misapplying our correct representation. These proliferate to the corners of the teaching profession via the weak ties network and swamp the system with this newly defined and exemplified version. 

Both stages contribute to a shift in the definition of this technique, either at a local or national level, stage 4. This definition shift might only be slightly changed from the original but crucially feeds back into the cycle and the process begins again. Each cycle moves the definition until a version is established that is noticeably less effective than the original idea, either due to its increased specificity (for example dual coding) or ironically, its lack of specificity (every type of coaching is suddenly instructional coaching). 

How can we avoid this?

Honestly I’m not sure. It took me about 5 months to get this far. I do think in an ideal world people would engage with a concept in detail, reading widely from a range of sources to understand it well, and debating the various interpretations but I also know everyone is busy. 

My thoughts so far involve a couple of things I think I will do to avoid my own contributions, both at my school and online.

At my school:

While I will accept that there is more than one good way of doing something and things look different in different subjects. I will be assertive and precise about what the most important features of a technique I am helping a department develop is. Probably by increasing the number of examples and non-examples I used.


I will welcome critical feedback on the things I share and try my best to acknowledge when I am wrong. When I change my mind I will explain clearly why I have, trying my best to use evidence and examples to support my change. Though I might come across as smug I will continue to write about what I consider optimal practice and justify that accordingly.

When I explain a new idea I am trying I will do my best to ensure I include the justification as to why I do it this way to illustrate the things I considered when making my choice.

Is there a lethal mutation occurring in ‘lethal mutation’?

I asked EduTwitter what they thought were lethal mutations and received a long list. 

Re-reading this list I think quite a few of the suggestions are not really lethal mutations (yet??). I think the term itself is probably being misapplied to mean “Things people do in a way I disagree with” or “technical terms used incorrectly by a lot of people” I think it’s important to keep this in mind. I am really only talking about things that by the mutation occurring potentially reduce student learning. While I’m sure you could say that anything suboptimal is harming student outcomes I’m not sure most count. So to me I am focused on things that are due to inspection frameworks (that take time away from teachers planning lessons to fulfil proxies), things done in nearly every lesson that are suboptimal and unnecessarily complex resources which incur a large opportunity cost. Everything else I don’t think has a significant enough negative impact to be considered a lethal mutation. So some of my examples used in this blog aren’t really lethal mutations in my opinion, but others disagree. Overall, I don’t think there is a lethal mutation in the term ‘lethal mutation’, while it is often used incorrectly the consequences to students are minimal so I think its better not classify it as a mutation.

If you have read this far then I thank you for your stamina. I hope you found this interesting and possibly helpful. I’d love to know your thoughts.

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