Interleaving is when you switch between different ideas or topics whilst studying, rather than studying ‘blocks’ of the same topic.
Conventional teachers tend to teach in ‘blocks’. For example, in Maths, teachers tend to set exercises consisting of 50 questions that are very similar. Whilst repetition is vital, research suggests that a more effective strategy is mixing out practice of one topic with other different, but related topics. For example, rather than completing 20 similar questions in a row, a better strategy would be to do a couple in a row and then complete a couple of questions from a related topic, then come back to the initial questions again.
You might be wondering why this works? Because learning is deeper and more durable when it is effortful. By forcing the student to switch to a different topic, they have to think harder and more critically when they comeback to the first topic, as opposed to just acting on ‘autopilot’.
A side-effect of this is that students will likely get more questions wrong. However, this is actually beneficial for their learning, because when they see the correct answer they will understand the strategy behind it better over time.
Hopefully you are starting to get the idea now.