Interleave Topics, Don't Block
Kornell and Bjork found mixing topics produces stronger retention than finishing one before moving to the next. Blocked practice feels organised; it produces weaker retention. Discriminating is the mechanism.
The strategy, as published
Exactly as it appears on the card
Part of Spacing & Interleaving in 01 Retrieval Practice, where it sits alongside its neighbouring strategies, the infographic and the thinking for the whole area.
Why you might use it
The problem it may help with
Blocked practice, finishing one topic before starting the next, feels organised, and pupils working through a block feel fluent. Kornell and Bjork found the feeling misleads: mixing topics produces stronger retention than blocking them.
The card names the mechanism: discriminating. When question types arrive shuffled, pupils must first decide what kind of problem they are looking at, and that decision is exactly what blocked practice never asks them to make.
What it might look like
One version of it, in a classroom
A maths teacher setting practice on area swaps a page of fifteen area questions for a mixed set: area, perimeter and volume shuffled together. Pupils now have to choose the method before applying it. The work is slower and scrappier than the blocked version; the choosing is the added ingredient.
Try it
A way to begin
Shuffle one existing practice set so that two or three related topics arrive mixed. Topics pupils can genuinely confuse give the discrimination something to bite on.
What to notice
Reading what happens
- Accuracy dipping during practice. Kornell and Bjork's point is that the dip in the lesson and the gain in retention tend to arrive together.
- Whether pupils pause to classify a question before answering it. That pause is the mechanism working.
Things to think about
Before and while you use it
- Tell pupils why the practice feels harder. Without the explanation, interleaving reads as disorganisation, to them and sometimes to observers.
The wider thinking
Where the evidence sits
Kornell and Bjork's studies established the effect, and Rohrer's work in mathematics classrooms has tested it furthest from the laboratory. The card’s attribution stands as published: Kornell & Bjork; Rohrer.
The fuller picture, sources included, is in further reading and evidence for Retrieval Practice.
Keep exploring
Where next?
Back to this strategy in 01 Retrieval Practice, across to what you're trying to improve, or into all 144 at once.
Want to take this further?
Support is available
Pedagogy First gives you a starting point. If you want support exploring how approaches like this can work across your school, trust or professional learning programme, that work is available.