Practice can be blocked: all of one kind, then all of the next (AAA BBB CCC). Or it can be interleaved: kinds mixed together (A C B B A C B A C).
In 2007, Doug Rohrer and Kelli Taylor had college students practice finding the volumes of four kinds of shapes. Blocked students did better during practice, about 89 percent right against 60 percent. But on a test a week later, the mixed students scored 63 percent and the blocked students only 20 percent.
Key idea
Interleaving: mix problem types or subjects in review. You learn not only how to do each kind, but which kind a problem is.
Worked example: Worked example
Which review set is interleaved?
- A: 5 addition, then 5 subtraction, then 5 multiplication.
- B: 15 problems with the three kinds shuffled together.
- B mixes the kinds.
Answer: B.
Why it works
With blocked practice you know the method before you read the problem. Mixed practice makes you choose, and choosing is the skill a test asks for.
Common mistake
Mixing on day one of a new skill. Learn the new kind first, then mix it into review.