Transform your teaching of difficult chemistry concepts with these ideas from cognitive science

Many hands juggling many balls

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The juggle is real – it’s more difficult for students to grasp a concept when there are multiple elements that interact

Understanding cognitive load theory (CLT) has helped transform my teaching, especially in recognising how to manage the transition from the need for teacher explanation to independent working. This is a critical point of the lesson which, if managed successfully, frees me up to move around the classroom to support students, ask questions and check understanding. If this transition is misjudged a lesson can quickly descend into an unwelcome game of whack-a-mole as I navigate the room with increasing speed as hands pop up and students utter phrases like, ‘I don’t know what to do’ or ‘I don’t understand’.

Four reasons for a misjudged transition

If we are to step back and diagnose the whack-a-mole issue, here are four reasons why it happens.

  1. Unclear instruction
  2. Challenging subject knowledge
  3. The explanation and examples are not related
  4. The students can’t keep up

I am going to share how I have used CLT to try to minimise the whack-a-mole phase of a lesson. If you need to further your understanding of CLT then I recommend you read these informative articles on lessons from cognitive science and reducing cognitive load.

Let’s look at how you can use CLT to minimise the whack-a-mole phase of a lesson. The first thing to consider is the inherent difficulty of the information that is going to be learned. This is the intrinsic cognitive load. Writing word equations is intrinsically easier than the construction of half-equations, which, I would argue, is easier than dynamic equilibrium.

The first thing to consider is the inherent difficulty of the information that is going to be learned. This is the intrinsic cognitive load. Writing word equations is intrinsically easier than the construction of half-equations, which, I would argue, is easier than dynamic equilibrium.

The way the content is presented can have a detrimental effect on working memory capacity

The inherent difficulty of a concept is increased when there are more elements that interact. For example, dynamic equilibrium is an abstract concept which has many steps that need to be sequenced. It requires prerequisite knowledge of reactions, an understanding of the term equilibrium, and knowledge of the different conditions such as pressure, temperature and concentration, as well as how these can affect the direction of the reaction. The working memory has a limited capacity and, with more challenging concepts like dynamic equilibrium, the working memory needs to hold more elements, which increases the cognitive demand on students. It is simply harder to learn than writing out word equations.

1. Teacher instruction and explanation are not clear

1. Unclear instruction

Under these conditions, it is essential that you break the concept down into more manageable chunks, which reduces the demand on the working memory. A teacher with better subject knowledge is more likely to be able to do this. When I watch non-specialists teach topics like dynamic equilibrium, it is often clear that they lack an understanding of what has to be taught and are therefore not clear as to how students are supposed to demonstrate their learning. This is because the demands on the non-specialist working memory are also high, which often leads to poor explanations.

For more difficult concepts like dynamic equilibrium, it’s helpful for non-specialists to have access to pre-planned lessons to help them deliver the content as a specialist would. It reduces the demand on their working memory and, just as important, ensures that the students are exposed to the information in a tried-and-tested way.

Another consideration is how you model the concept. Extraneous cognitive load, for example the way the content is presented, can have a detrimental effect on working memory capacity. It can be useful to provide a worked example, which can be defined as a problem statement and the appropriate steps to a solution. Going through these steps can reduce the demand on the working memory. Design and practise a worked example before teaching it. Be aware that a poorly constructed worked example can increase undesirable extraneous load and reduce student access to the work. You could run it by a colleague who is a subject specialist to be sure you minimise this risk.

2. The subject knowledge is challenging and not yet secure

2. Challenging subject knowledge

You also have to respond to the emerging needs of the students when teaching a concept. This means having the freedom to reteach and not be beholden to a lesson plan. When checking for understanding, if students’ subject knowledge is still not secure then there is no point in moving on. Reteach the material and check for understanding again. This should be seen as a strength of the teacher, as opposed to a weakness of sticking to the lesson plan. If student understanding is not secure, their working memory is more likely to be overwhelmed and they will struggle with the next phase of the lesson.

3. Questions do not reflect the examples in the teacher explanation, or are too hard

Having taught a concept using a worked example, some teachers can then make the fatal mistake of giving students questions which bear little resemblance to it. The students are expected to transfer their newly acquired knowledge to a new situation which is cognitively demanding. To avoid this, the teacher should make sure that the students’ question reflects the worked example and builds up in difficulty gradually. The teacher might also use partially-completed worked examples to act as scaffolds and reduce the intrinsic difficulty for the students. As students experience success, these scaffolds can be taken away.

It is also important to provide students with multiple questions to enable them to move beyond a basic familiarity with the material. It’s a mistake to ask the students to answer only a couple of questions before giving them a complete exam question. This can also initiate a whack-a-mole phase in the lesson: the exam question is cognitively too hard and the students are not ready to answer it. It’s preferable to work towards fluency before expecting students to transfer the information to more complex questions.

4. There is a perceived pressure to move from teacher-led to student-based learning before the students are ready

4. The students can’t keep up

Finally, because some concepts are much harder to teach and learn than others, they require more teacher input. This means that a teacher should not be worrying about obtaining student-independent learning within a single lesson. Across a sequence of lessons, when the students are ready, they can and should be given the opportunity to work on their own.

For further background and information on cognitive load theory, read these informative articles on five invaluable lessons from cognitive science ( and reducing cognitive load (

Dom Shibli is module leader for the secondary science PGCE and a senior lecturer at the University of Hertfordshire