In neuroscience this concept is thought to work because our brain thrives on problem solving. This method essential helps the brain by improving its ability to discriminate between concepts. With interleaving, each practice attempt is different from the last, so your brain must continuously focus on searching for different solutions. That process can improve your ability to learn critical features of skills and concepts, which then better enables you to select and execute the correct response.
Another reason why this is thought to work is that interleaving strengthens memory associations. With interleaving — the correct solution changes from one practice attempt to the next. As a result, your brain is continually engaged at retrieving different responses and bringing them into short-term memory. Repeating that process can reinforce neural connections between different tasks and correct responses, which enhances learning.
Add to this method the element of rest at key intervals as I outline in this article, and you become a learning machine.