Doug Lemov's field notes

All of our recent TLAC books include discussions of a graph that all teachers should know about: the ‘Forgetting Curve.’ It describes how learners forget things over time and how retrieval practice can arrest this process.

The original Forgetting Curve was derived in the 1880s by the German psychologist Hermann Ebbinghaus and plotted the actual rate at which he was able to remember a series of nonsense syllables after learning them. The general shape of the curve is broadly accepted by cognitive psychologists. But since your students aren’t learning nonsense syllables, the rate at which they forget what they have learned after they learned it is less clear. So what the  Forgetting curve tells us that:

• as soon as you achieve some understanding of an idea , you begin forgetting it almost immediately. It starts to fade.
• the rate of forgetting is often shockingly high; a few hours after learning something, people routinely remember only a small fraction of it.
• learning–defined as ‘a change in long term memory’ is different from understanding but with the latter often mistaken for the former. But learning is what’s left over after forgetting takes its toll on what we (or our students) briefly understand.
• each time you practice recalling what you know, the rate and amount of forgetting is reduced somewhat.
• retrieving something back into working memory slows the rate of forgetting, but how and when the retrieval happens is important.

A Forgetting Curve cannot tell you exactly what the rate of retention will be for your students generally or for a specific student at time A or time B for a specific topic you’ve taught. There are individual differences and factors in the learning environment, like how much attention students are paying and how new to students the information is/ There are differences in content too: abstract and complex ideas; simpler and more concrete.

So the curve in is also theoretical or hypothetical in any specific case.

And it also leaves open what the magic number of times students have to engage something to learn it. Graham Nuthall’s Hidden Lives of Learners proposes that whether a student was exposed to content three times can predict with 80-85% accuracy whether they successfully learned it.

Of course there are settings in which we need far better than 80% accuracy… or where we need faster retrieval… where it has to be instantaneous.  In those cases the required number of retrievals will be far above three.

So the Forgetting Curve is a highly useful and also imperfect tool but one educators should know.

That said it’s actually complex to read one the first time you encounter it and I get questions from educators about it all the time. So as part of TLAC 3.0 we have included an ‘annotated’ Forgetting Curve… one with descriptions build in so it’s more portable and how to read it is more readily apparent. Here’s a draft in case it’s useful first the annotated curve:

And then a clean version:

I’ve temporarily adapted both from a drawing of it the amazing Oliver Caviglioli made for CGT. Hope its useful!