Mix it up when practising

The idea in one sentence: practise different kinds of problem mixed together, not one kind at a time, so people learn to spot which kind they’re facing. It feels harder and slower, but on a later test it usually does better.

You’ve seen this already

Think about learning to cook. A recipe book groups things: all the soups, then all the cakes. But on a weeknight you open the fridge and have to decide what to make. Nobody has told you it’s a soup night. That decision is a skill, and you only practise it when the choices are mixed.

Or think about sport. A tennis coach can feed you twenty forehands in a row. You’ll look great. In a match, the ball might come to your forehand or your backhand, and you have to choose. Mixed drills feel messier, but they train the choice.

Why it matters for your teaching

Healthcare teaching often comes in neat blocks. Three chest cases, then three heart cases. Five questions on one drug, then five on the next. Inside each block, people do well, because the heading has already told them what kind of case it is.

Real work doesn’t come labelled. A breathless patient might have a lung problem, a heart problem or something else entirely. A paramedic, a nurse or a physio has to work out which before they know what to do. If spotting the difference is part of what people need to do differently, they need practice at spotting it.

So, mix it up. In a case review, put different kinds of case side by side. On a pharmacy teaching round, mix questions on drugs that look alike or sound alike. Ask “which is this, and how do you know?” before “what would you do?”

People will find this harder. They may say the session felt muddled. That feeling of difficulty is normal and doesn’t mean it isn’t working. Tell them so at the start.

Try this

• Shuffle your cases. Instead of a block of one kind, mix two or three kinds that are easy to confuse.
• Ask “which one is it?” first. Get people to name the type of problem before they solve it. That step is the skill blocks leave out.
• Warn people it will feel harder. Blocked practice looks better during practice; mixed practice usually does better on the test afterwards. Say this out loud, so people don’t give up.
• Mix in older material. When you return to a topic, mix it with something newer, so people have to choose between them.

How sure are we?

The evidence is good but more mixed than for retrieval practice or spaced practice. A large review that pooled 59 studies (Brunmair & Richter, 2019) found a moderate benefit on average. The benefit was largest when people had to tell apart things that look similar, such as paintings by different artists. It was smaller for maths, unclear for reading texts, and for learning lists of words, blocks did better. Another major review (Dunlosky et al., 2013) rated it as only moderately useful, because there was less research.

Most studies were in labs or school maths. There is little testing in clinical settings, so we can’t say how much it helps at work. There are good reasons to expect it to help, because telling cases apart is a key clinical skill. Note that interleaving means mixing kinds of problem. Simply switching between a quiz, a talk and a video is not the same thing.

Where it comes from

Sports scientists noticed something similar with physical skills in the late 1970s. In 2007, Doug Rohrer and Kelli Taylor showed that shuffling maths problems helped students solve them on a test a week later, even though shuffled practice felt worse at the time. In 2008, Nate Kornell and Robert Bjork had people learn the styles of different painters. Mixing the paintings helped people recognise new paintings. Yet most of them believed the blocked way had worked better.