You are currently viewing Interleaving: One Strategy to Recover Lost Learning

Interleaving: One Strategy to Recover Lost Learning

Interleaving is a memory strategy that has great potential for impact – as long as it’s embedded in the classroom. Glenn Whitman and Dr. Ian Kelleher explains what it is and how educators can integrate it into learning.

We love what we teach. Whether it is history for Glenn or Science for Ian, we both think our subjects are exquisitely important, and quake at the thought of sending our students into the world with only spotty knowledge of the American Revolution and Newton’s Laws of Motion.

Since March of 2020, when we suddenly found ourselves in what Paul Kirschner termed “emergency remote teaching,” we have had to make choices about the content we love. Whether in remote, hybrid, concurrent, or in-person school, we immediately recognized that the ability to meet our normal content coverage and learning objectives was significantly reduced. 

In many ways, a crisis has created an opportunity. Most teachers are reluctant to give up any of their content. “It is all important,” they say. But let’s flip that deficit mindset, especially as we know that “covering the content” does not mean that students are actually learning the stuff we want them to retain and are able to transfer it to new learning scenarios and life experiences.

“Well, I covered it” is a terrible benchmark for teaching and learning, this year more than ever. Instead of thinking about what we are not teaching, let’s take this opportunity to focus on what is truly important in our subjects and endeavor to teach it in ways that make it durable, usable and flexible in the minds of our students.

There is a significant equity aspect to this too. It is being projected that historical trends of learning loss based on class and race will be exacerbated the longer students are fully remote and away from their schools. (1,2) Individual and small group tutoring, spaced out over time, is showing promising results to alleviate this, but the resources this requires means it is often hard to do. We need some simple techniques that every teacher can implement in every classroom.

In addition, while learning loss is bad, perhaps even more concerning is the social, emotional, and mental health impact of COVID-19. This should serve as a reminder that school and learning is a social, emotional, and cognitive experience. This has to be central in our mind, whatever we plan to do. 

How do we efficiently build robust memory?

Maximizing the learning from a disrupted school year relies a lot on the skills of the teacher. Here is where the science of learning might provide a promising strategy.

A lot of important, teacher-friendly books and resources have been developed over the years to elevate teacher understanding and application of memory strategies in the classroom, such as spacing, self-testing, and interleaving. The CTTL’s work in this area was sparked by McDaniel, Brown, and Roedeiger’s “Make It Stick.” Since then, books like “Powerful Teaching,” “Retrieval Practice,” “How We Learn” (to name a few), and the resources provided by The Learning Scientists, Learning Agency Lab, and Cult of Pedagogy, have been important guides to help elevate teachers’ understanding of “next-day applicable” memory strategies.

Of all these memory strategies, we are especially intrigued by interleaving. It has great potential for impact but can be daunting to implement. Students are highly unlikely to use it unless their teacher embeds it in their class. And this is the perfect time of the year to embed it – far enough into the school year to have a lot of material to work with, but far enough from the end so there is plenty of time to really work at it.

Many teachers are introduced to interleaving by comparing it to a traditional “massed” or “blocked” sequence of units, usually along with an image like the one below (3):

This image shows two charts, one showing the traditional sequence of massed units, and the second showing the sequence of interleaved units.

Images like this are common in articles and blogs. But what does this actually look like in your context with your subject and your students?

It starts with identifying the core ideas, facts, and skills. Ask yourself, “What do you want your students to still know and be able to do in two years time?” Then, identify places where you can bring these ideas, facts, and skills back.

Yes, the students will get rusty, and the effort of trying to recall them may be a bit painful, but that is the point. This deliberate difficulty is what makes it work.

Here is one example:

Interleaving in practice

Glenn teaches “United States/European History to 1860” to 10th grade students. The class does a thorough study of the origins of the 13 colonies. A chance to interleave and further embed these origin stories into a student’s long-term memory occurs when students are asked, “How are the Articles of Confederation, Constitution, and Bill of Rights a logical outgrowth of America’s colonial experience with England?” 

Similarly, Glenn made the strategic decision to not teach the 1676 rebellion led by Nathaniel Bacon, considered by historians as “The Torchbearer of the American Revolution” in its chronological place in history. But when the class moved forward 111 years to Shay’s Rebellion, the opportunity not only emerged to interleave the teaching of Bacon with the teaching of Shay, but it also allowed for what he calls “primed interleaving” by introducing the forthcoming Whiskey Rebellion of 1794. 

Finally, when Glenn teaches, and the students deeply study, the Declaration of Independence, it also creates the opportunity for “primed interleaving” when the students discuss how “all men are created equal” was integrated into France’s Declaration of Rights of Man and Citizen (1791), the Declaration of Sentiments (1848), and the Vietnamese Declaration of Independence (1954).

A general strategy

So, what are some steps to strategically elevate the promising research-informed strategy of interleaving into your pedagogical practice, especially during this complex school year?

Start with this thinking routine:

  • Look left. What are the big ideas from last year that your students should know but might not? Set a timer for two minutes and make a list.
  • Look right. What are the essential skills, ideas, and factual knowledge that students need from your class in order to be successful next year? Again, set a timer for two minutes and make a list.
  • Look up and down. Think back on all that you covered so far this year. What do you really hope your students know? What do you really hope they can do? Once more, set a timer and make a list.

Research suggests that even in normal school years, teachers have a very hard time accurately judging what their students know and can do. This year it has to be harder still. So plan a series of short formative assessments spread over the next two to four weeks to find out (either no-stakes or by giving a few points that can be earned by putting in good effort).

Use what you listed above (left, right, up and down) to write these formative assessments. Include key ideas and skills more than once.

This type of recall is hard, and emotional support for students is critical. Talk to your students about how you are letting them get rusty on purpose, that trying to recall will feel hard, but that the effort they put in trying to do so will ultimately help them remember. Tell them you are expecting them to get many things wrong or partially right, and reassure them that getting things wrong right now will not count against their grade. This is all about building the foundation to get better grades with less effort later.

Do short bursts of highly targeted reteaching where you find systematic gaps, and create practice and review assignments where students are rusty. Use a tool like Loom or Screencastify to make two-minute videos that cover key points. The ability to see your face, particularly during distance learning, carries power! 

Repeat this process in the upcoming months, constantly using the formative assessments to recalibrate your thinking about what students know and can do, and thus what you need to ask them about next.

If possible, plan your final year summative assessment, whether it is an exam, a project, or some combination of both, around the insights you have gained from this process.


In closing, we know that each student’s academic recovery from COVID is an extended process and will vary by individual. And there are no easy solutions. But leveraging research-informed strategies such as interleaving can help. There has been no greater challenge in our careers than teaching in the midst of a pandemic – and yet within this there are moments of opportunity where, out of necessity, we might reimagine and elevate our practice. Let us know what it does for your teaching and your work with your students.


1. Dorn, E., Hancock, B., Sarakatsannis, J., and Viruleg, E. (2020). Achievement gap and coronavirus, McKinsey.

2. Mitchell, F. (2020). COVID-19’s Disproportionate Effects on Children of Color Will Challenge the Next Generation. Urban Institute.

3. Think Differently and Deeply, Volume 3 (2018). The Center for Transformative Teaching and Learning.

About the Authors

Glenn Whitman is the co-author of “Neuroteach: Brain Science and the Future of Education” and directs the Center for Transformative Teaching and Learning at St. Andrew’s Episcopal School. Glenn is a former Martin Institute for Teaching Excellence Fellow and author of “Dialogue with the Past: Engaging Students and Meeting Standards through Oral History” as well as co-editor of Think Differently and Deeply, the international publication of the CTTL. Glenn earned his MALS from Dartmouth College and a BA from Dickinson College.

Dr. Ian Kelleher is a science teacher at St. Andrew’s Episcopal School, and Head of Research for its Center for Transformative Teaching & Learning. His work focuses on helping teachers translate the science of learning into everyday practices in their own classrooms, and measuring the impact. Ian is the co-author of “Neuroteach: Brain Science and the Future of Education,” and co-designer of Neuroteach Global. Ian is the the inaugural Joseph and Kathleen Dreyfuss Faculty Chair for Research, an endowed position at St. Andrew’s Episcopal School for the lead CTTL researcher.