Anyone over 30 years of age has probably had the experience of trying to learn a phone number. This is a dying art in the age of smartphones; if you haven't had the experience, just try to imagine it. When you tried to learn a new phone number, did you re-read it again and again hoping that you would remember it? Of course not. Rather, you said it over and over again until you used it. To learn the phone number, you used a technique known as ‘retrieval practice’ (although you probably didn't know what it was called). Another term for retrieval practice is ‘test-enhanced learning’. Test-enhanced learning refers to the increased retention of knowledge or skills that is produced by the act of retrieval during testing. Although tests improve learning by increasing motivation and efficacy of studying (indirect effects), the increased retention that derives from retrieval itself is known as the direct effect of testing. This effect occurs even without feedback.1 If you think about learning the phone number, you realise that it is the act of repeating it back to yourself that really makes it stick; checking your source simply ensures that your retrieval practice is accurate. In medical education, however, the material is often complex and retrieval errors are common, so feedback is an important source of learning. Research in test-enhanced learning shows that feedback greatly amplifies the retention produced by testing.2 While we're talking about learning phone numbers, it's important to acknowledge that any activity that promotes retrieval constitutes a form of testing. As we repeat the phone number, we are testing ourselves. When we think of tests broadly in this way, it becomes apparent that retrieval practice can be applied to a variety of learning situations that pertain to both knowledge and skills. Tests (or retrieval practice) can come in the form of oral quizzing during hospital rounds, simulated resuscitations and even informal discussions about patients. Learning a phone number is an example of rote learning; however, it is important to recognise that increased retention of knowledge through testing has been shown to improve the transfer and application of knowledge.3 Going back to the phone number, if we were to repeat the number to ourselves just once, would we remember it? No. So we repeat it over and over. The same holds true for other forms of learning. Repeated testing is likely to produce better retention than single testing.4 Repetition isn't the only important factor, though. We must also consider spacing. If we repeat the phone number 10 times back-to-back, are we likely to remember it in a month? No. We will remember it long enough to dial it, but it will probably be gone before the day is out. Research in cognitive psychology indicates that retrieval practice (or testing) needs to be spaced over weeks and months in order for learning to be retained for years.5 In fact, we have probably all had the experience of dialling a phone number again and again over time until our fingers move automatically to the numbers. We almost never forget those numbers. It's interesting to consider, though, how we forget numbers in our smartphones because we don't practise retrieving them. By thinking about the different forms of retrieval practice, using repetition and spacing, and providing feedback, teachers can plan for retention rather than simply assuming that it will happen. Educators should call upon (pun intended) test-enhanced learning as they consider how to help their students retain the knowledge and skills they will need to care for patients.