We understand that difficulty and the effort it requires from the learner are essential for learning. But how do we find the appropriate level of difficulty? If it's too low, the learner makes no effort and learns nothing; if it's too high, the learner experiences cognitive overload and may become discouraged.
Several studies suggest that the optimal level of difficulty is slightly above what the learner can handle without external assistance. The aim is to offer the learner a small step beyond their current capability. For example, the next stage for an actor who can recite their lines flawlessly might be to recite the same lines with emotion; for a salesperson who can sell their product to a receptive client, it could be presenting the same product to a reluctant customer.
These types of challenges are said to fall within the Zone of Proximal Development: learning is most beneficial when the activities proposed in your course or training are situated in this zone.
To consistently reach the Zone of Proximal Development, you need to be able to control the level of difficulty on demand, which involves understanding where learning difficulties originate. The primary factor influencing difficulty is the gap between the learner's current level of mastery and the task to be accomplished. Therefore, if you have detailed data on your learner's initial level (notably through feedback), you can adjust the task to modulate the level of challenge in your training—for example, by removing access to certain hints, integrating previously covered concepts, or adding a time limit to your questions.
🎯Alternating Concepts: an example of atteignable difficulty
One of the most effective ways to modulate difficulty is to alternate the concepts to be learned. For instance, in tennis, it's better to learn by regularly alternating between forehand and backhand strokes (interleaved practice) rather than practising a hundred forehands followed by a hundred backhands (blocked practice). Similarly, if you want to be able to recognise a Van Gogh painting from a Cézanne, it's better to alternate between the works of each painter.
Alternating learning forces the learner to recall concepts they have previously seen ("What did the Van Gogh painting look like?"). Meanwhile, they will have worked on another concept, creating contextual interference with what they are trying to retain ("Am I confusing it with Manet?"). Overcoming these interferences requires greater effort from the learner—a desirable difficulty that strengthens the long-term anchoring of learning in memory.
🎓 Clearing forgetfulness, step by step
Why do we learn better by alternating, even though we make more mistakes initially? In reality, the effort the learner must exert to overcome the interferences caused by alternation helps them clear the access paths to the concepts stored in their memory.
Imagine that our memory is like a forest crossed by numerous paths. These paths are the mental traces of our learning, which vegetation—forgiveness—gradually overgrows.
Suppose we walk only and for extended periods on the path corresponding to a single concept: meanwhile, the paths corresponding to other similar concepts will have become entirely overgrown, and our mental traces to access them will be less robust. Conversely, in interleaved learning, we regularly walk each path, removing the vegetation as soon as it appears.
Keywords: optimal difficulty, Zone of Proximal Development, cognitive overload, interleaved practice, desirable difficulty, contextual interference, memory anchoring, e-learning strategies, learner engagement, instructional design.
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