The Curse of Knowledge: when we are given knowledge, it is impossible to imagine what it’s like to lack that knowledge. Chip Heath, Made to Stick

How much do teachers need to know? In my last post I proposed that an effective teacher – one who is warm, friendly and a great speaker – is minimally effective if they have nothing to teach. The Dr Fox (or Ken Robinson) Effect shows that even though we love charismatic teachers, we don’t learn much from them unless they are also knowledgeable about the subject they’re teaching.

Following a prolonged and protracted debate with headteacher Jonathan Taylor I’ve accepted that images (1)the relationship between teachers’ subject knowledge and student achievement is probably ‘curvilinear.’* That is to say, although there’s a minimum level of subject knowledge teachers need to have in order for their students to be successful, increases in subject knowledge appear to lead to declines in students’ outcomes. This is probably similar to the findings of Inverted U Theory: that while some stress is desirable, too much will adversely affect performance.

This kind of curvilinear relationship makes intuitive sense for stress, but why should it apply to teachers’ subject knowledge? Well, try the following experiment for size: tap out the melody to a number of popular songs and estimate how many will be recognisable to a listener. In a study by Elizabeth Newton, it was found that subjects overestimated the ability of another person to recognise the melodies by a factor of 20. When you know something it is very difficult to think about it from the perspective of someone who doesn’t know it. As physicist Carl Weiman puts it, “well intentioned physicists are achieving poor educational results because the “curse of knowledge” makes it very difficult for them to understand how physics is best learned by a novice student, or to accurately evaluate that learning.”

Recent advances in neuroscience have demonstrated that we actually think very differently when we think about a subject we expert in to one where we are a novice. A study from Nicole Hill and Walter Schneider confirms that as we learn, our brain’s architecture changes and thoughts are processed differently; as we move to mastery, our brains form different links, so that it becomes possible to observe different activation patterns during problem solving. Not only do experts and novices think differently, it may be that the very knowledge which makes us experts acts to prevent us from understanding how novices perceive and process the material we’ve already mastered. This may cause us to make mistakes about how students are likely to learn. In Ouroboros, Greg Ashman points out that, “people think that authentic, real-world projects will be motivating …  teachers routinely underestimate what is required to complete a task because they are suffering from the curse of knowledge.”

The ‘curse of knowledge‘ is a real and pernicious cognitive bias; the more expertise we develop, the less empathy we may have with their students. So, how much do teachers need to know to be optimally effective? After all, it may be that most teachers are not yet at the point where the relationship between what they know and how their students learn has reached the point of the curve where their knowledge has become a curse. Before you get too excited about all this, it really won’t help students for their teachers to know less.

In order to best understand the relationship we would be well to unpick the differences between ‘mere’ subject knowledge and pedagogical content knowledge. I’d argue that the latter must include the former but, added to the wealth of understanding a great teacher ought to have about the subject they’re teacher, they also need to know about how novices learn the subject. Teachers’ subject knowledge ought to include knowledge of the threshold concepts of their subject and a thorough knowledge of common misconceptions and how to help students suppress them.

Ironically perhaps, this is a call for teachers to know more, not less about their subjects. We need to need to become experts in how our subjects are learned as well as taught.

* This proves once and for all that Twitter really can be an effective tool for debate if all involved are prepared to be reasonable and learn from each other.