cascade failure

When we no longer allow learning to become forgetting, there are two possible outcomes, when we use increasing interval retrieval practice, responsive to the need for feedback:

(1) Learning becomes more deeply embedded in long term memory(2) Learning doesn't become more deeply embedded in long term memory
... this is the desired outcome.... this is the cause of cascade failure.
When we teach a layer of learning within the learner's "sweet spot", neither too easy nor too hard, something but not too much, the learner can learn.If we teach "too hard" or "too much" the learner's working memory is overloaded - they can't learn easily or they can't learn at all.
Each time the learner practises that layer, provided we allow some but not too much forgetting to happen, they embed the layer more deeply in their long term memory. Each time the learner practises that layer, even if the learner gets enough help and feedback, we may see the learner gradually learning or we may find the learner can't learn at all.
The learner can remember the layer for longer each time and they need to practise that layer less frequently.The duration for which the learner can remember part or all of the learning may increase very gradually - so over time they need less help - or the learner just can't remember, they always need help.
The fraction of lesson time required to practise each layer of learning decreases over time.The fraction of time required to practise each layer either decreases slowly or doesn't decrease at all. 
As we teach more layers of learning, each at the learners sweet spot, there is sufficient lesson time to do enough practice. All learning can be practised close enough to optimal intervals that all learning is retained.

As we teach more learning which is too hard or too much, there is

  • insufficient lesson time to do enough practice, 
  • so some practice happens too late,
  • when the learner tries to do the too late practice, they need help,
  • but there is not enough teacher capacity to give sufficient help, 
  • the learner can't practice without the help, 
  • so even learning which had been learned is forgotten and needs to be practised more frequently,
  • so there is even less lesson time for each practice and even more that needs practising,
  • etc. etc This is cascade failure.
When the teacher comes to create the timely practice assignments, only a small number of layers are fragile.When the teacher comes to create the timely practice assignment an ever increasing proportion of the layers are fragile.

To avoid cascade failure:-

In other words use timely practice as it was designed to be used.

The solution to cascade failure:-