Customer Knowledge Baseincreasing interval retrieval practice or spaced repetition system (SRS)

increasing interval retrieval practice or spaced repetition system (SRS)

Education researchers usually now talk of increasing interval retrieval practice whereas spaced repetition system is favoured by computer programmers.

An increasing interval retrieval practice or spaced repetition system (SRS) is a method to increase memory retention by multiple timely reviews.

What teachers generally call retrieval practice and researchers generally call spaced learning relies on the what is called the spacing or testing effect - if we practice something after some, but not too much forgetting has happened we will increase the duration of the retention.

We are all forgetting all the time

Hermann Ebbinghaus (1885), did experiments to find out how we forget.

He called the graph below die Vergessenskurve or in English the forgetting curve.

It shows that as time goes on, memory fades. 

This graph shows several peoples' forgetting curves.


The graph shows the forgetting curve for people with very weak, weak, below average, average, above average, good and very good memories.

When we review knowledge, we will remember it for a longer period of time 

Each time we review the knowledge (provided we haven't already forgotten it) it will last for longer before we forget it again.

A spaced repetition system, uses this to help us remember for longer

If we can review the knowledge, just before we are about to forget the knowledge, we can maximise the length of time we remember the knowledge for and minimise the number of reviews. This is what an SRS does.

The graph shows

  • very weak memory being reinforced for the 1st time on day 1

  • this weak memory is reinforced for the 2nd time on day 3

  • the below average memory is reinforced for the 3rd time on day 7, 

  • the average memory is reinforced for the 4th time on day 15, 

  • this above average memory is reinforced for the 5th time on day 31, 

  • this good  memory is reinforced for the 6th time on day 63, 

  • this very good memory will persist beyond day 127, perhaps until day 155, unless it too is reinforced before then. 

There are other factors in memory retention as well as time

  • We know active review works better than just reading though. How lucky that answering a maths problem is actively reviewing, providing we are not reviewing exactly the problem we have done before. Merely repeating the same problem allows learners to take a short cut by just remembering the answer.

  • We know that making links within our brain, which is perhaps the same thing as learning things we understand, works better than trying to learn seemingly arbitrary nuggets of wisdom.

  • We know that there are other factors, which are harder to pin down involved in how fast our memory decays. 

Video on how the spaced repetition system works

This is the same video increaseLTMduration.mp4 found on the Explaining and Training page - you might want to watch the first 3 minutes.

Forgetting in low attaining classes.

If we think of a class of low attaining learners, often the characteristic the learners most have in common is that they forget easily. This makes teaching them hard, and learning for the learners very hard. The teacher can’t rely on what they have previously learned to build up new learning and the learners often remember best what they “can’t do”. Consistent use of the timely practice app will ensure learners remember nearly everything they learn, and when they forget, it will be quick and easy to remind or re-teach them. The app uses the spaced repetition system (SRS). The greatest advantage of SRS will be felt by low attaining learners. 

On the graph below we see the forgetting curve for 16 learners in a low attaining class. They have been taught a new skill, method or a few related facts, which I’ll call it. The f below the time axis shows when each learner would forget it, if they didn’t review it. Depending on when the teacher was to assess the learning of the class on it, she would see very different results.

After one day 13/16 remember, after three days 9/16 and after three weeks only 4/16 remember it.

Look at the retention of it for just one of the learners using 3 different systems.  

With the no review system, the learner forgets, what they have seemed to have learned in class within 2 days.

With the weekly review system, the learner learns some work, forgets what they seemed to have learned within 2 days, re-learns the work (as they have already forgotten the work it requires re-teaching and re-learning rather than reviewing), forgets again etc.

With the spaced repetition system, the learner reviews the work before it is forgotten. There is however a bonus, each time the work is reviewed before it is forgotten the memory strength increases and the learner will remember for longer. The graph shows the reviews, the vertical lines, at days 1, 3, 7 and 15. Notice the learner has, nearly but not quite, forgotten it before each review and that after each review the length of time that the learner can remember it increases. After the light blue review, on day 15, the learner will be able to remember it for over a month and after another four reviews, the learner will be able remember it for almost a year. 

The timely practice app is designed so that maths teachers will  to be able to get all their learners to review all their work in a timely manner.

Moreover the app is designed so that the teacher can “see” when their learners are ready to learn new, harder work.