science of learning: research meets practice
interleaving

School: Sky View Middle School, Leominster, MA
Teachers: Dr. Kim Kelly, Shannon Payette 
Researcher: Dr. Megan Sumeracki

Interleaving, or “mixing it up,” is a way to increase learning potential. By changing up problem types often, it helps students choose not just what to do to solve a problem, but how to choose a strategy and when. 

For example, instead of studying 10 multiplication problems, then 10 division problems, and then 10 addition problems, mixing those problems up helps students find and see similarities and differences between the different types of problems. It also helps to review older concepts and hone the skills needed to choose correct strategies for solving problems.

“What interleaving does is force the students to figure out not just how but also when” to use a specific problem-solving strategy, explains Megan Sumeracki, learning scientist. Sky View teacher, Kim Kelly adds that “they can’t get to the solution if they can’t get to the start,” pointing out that often fundamentals need a lot of support. 

Part of the skill of solving math problems involves applying the right procedure to the right problem. Interleaving develops that skill. Problems can look very similar, yet require different kinds of approaches. Interleaving often results in worse performance during the practice sessions, but far higher performance on subsequent tests.

Interleaving works because it involves the right kind of practice. Blocked practice means the student never has to think about which strategy or procedure to apply; interleaved practice helps students associate the right strategy with the right problem (among other things). 

To clarify, though, research doesn’t support an idea like “never do blocked practice”. Blocked practice is necessary for students beginning to understand a concept. Experts recommend aiming for interleaved practice at least a third of the time.

Both Kim and Shannon realized that interleaving their homework assignments and tests would require some extra time. Since most textbooks and worksheets featured blocked practice, they had to modify them. But, they both noticed the difference in their students’ problem-solving abilities.

After creating an interleaved worksheet, Kelly noticed that “students (were) stopping and thinking...their brain had to shift from this topic back to some old material.” Shannon saw improvements when she administered a standardized practice test. “I have a kid who has struggled. (He) did not meet expectations for math at all on his last year (state) test. He got 6 out of 6!”

Instead of always giving students problems involving the most recent concept students have learned, try incorporating a mixture of problem types into student homework, exams, and review sessions. This is particularly helpful for problems that look similar, but require different strategies, or for problems that look quite different, but can be solved with the same strategy.