When I started piano lessons at age five, I learned “songs” written for the right hand, and I learned to read the treble clef in music. 

Sometime later, my left hand was introduced to the keyboard, and I learned to read the bass clef. Even at a young age, I felt a troubling imbalance of power. My right hand had become strong and capable, and my left hand weak by comparison. I struggled to read the bass clef fluently. These disparities lasted for years. 

Much later, I would take tennis lessons, and in doing so spent the first several sessions working exclusively on my forehand swing. When it came time to rotate the racket and learn the backhand, I didn’t do nearly as well, and for as long as I played the game, my backhand remained weak and undeveloped. 

Years later again, I took a graduate course in field natural history. Each day, the class would hike in a different location, outfitted with notebooks and cameras, and our instructor would teach us to identify wildflowers, shrubs, trees, and occasionally insects. Our homework was to look up the family, genus, and species of each specimen in our textbooks, then take notes on the defining characteristics of each. It was challenging work, but even now when I go for a hike in the woods, I can still identify many of those species. Why?

The way I learned piano and tennis is referred to massed or blocked practice. In contrast, the way I learned field natural history was an interleaved approach.

Imagine wanting to learn about art history and starting with impressionist painters. Would it be better to spend an entire unit learning about Monet’s paintings before moving onto Dégas, Renoir, and Manet? Or might it be better to be exposed to all four artists in your first unit, diligently learning the characteristics of their paintings, subjects, and styles, and learning from the start to discriminate among them? Spoiler alert: It’s not going to be the one that sounds easier.

What is interleaving?

Interleaving is a powerful learning strategy that involves mixing or alternating the practice of different topics (or subtopics) or skills during learning or study. This is in contrast to focusing on one topic or skill at a time before moving onto the next. When you learn about all the painters initially or learn the piano using both hands from the start, that is an interleaved approach. The idea is that this variety of practice on different topics at once can lead to a deeper and more flexible understanding of the content. 

In the first art course scenario (blocked practice), you would become quite comfortable with Monet’s paintings during Unit 1, and learning might feel easy and fluid. In the second scenario (interleaved approach), you would feel more challenged, as if it were taking longer for you to become proficient at identifying each painter’s work. 

Diagram showing blocked vs interleaved practice with impressionist painters

Blocked practice (left) and Interleaved practice (right)

How does interleaving work?

One line of thinking is that interleaving forces us to engage in a form of “distributed practice” (aka the spacing effect) by switching among related but distinct topics or skills. If you’re learning about all four painters at once, there will be time between when you see one Monet painting and then another. And of course, spaced practice requires retrieval practice, which we also know strengthens the learning connections. (Yes, these learning strategies ALL related!) In contrast, blocked practice does not allow forgetting to seep in, and therefore doesn’t call for retrieval practice. A little forgetting is actually good for us! 

Another, similar line of thinking says that the more effortful retrieval is, the better it is for us. It signals to our brains that what we’re working so hard to remember is indeed important! Interleaved practice, with those “spaces” between learning one thing and the next (again, called distributed practice), is thought to lead to deeper processing. 

Interleaving strengthens our memory associations and specifically helps us differentiate among related topics or skills. We will more readily distinguish Monet’s short, choppy brushstrokes from Degas’ fluid, almost indistinguishable ones after learning in with an interleaved approach. This can result in greater retention and more durable and flexible learning. After all, we’ll want to take our newly learned skill of identifying Impressionist painters to many different art museums—read: apply our learning in unique places. When we learn in an interleaved approach or interleave our own study topics, we’re better prepared to apply what we know in a variety of contexts.

How can instructors, teachers, and trainers use interleaving?

  1. Introduce varied topics, subtopics, or examples within a session, lesson, or unit, ensuring that learners encounter different problem types or scenarios related to the broader topic.
  1. Create practice sets, assignments, or assessments that include a mix of content from different lessons or units.
  1. Integrate retrieval practice with questions. Ask questions during sessions that require learners to recall information from various subtopics covered in previous sessions.
  1. Encourage learners to make thematic connections among different subtopics or skills, highlighting their interrelatedness. Help learners see the broader context of their learning.
  1. Create contextual learning activities, such as real-world scenarios or case studies, that require learners to apply knowledge from multiple subtopics, fostering a holistic understanding of the broader topic.

Complement these interleaving strategies in your training sessions with any strategy requiring retrieval practice.