A really important question; how often do students need to encounter something to remember it? I first encountered this idea through Graham Nuthall's work and his estimation based on close examination of students thinking processes that students learn concepts when they encounter it three times (see passage) but it wasn't until I read the literature around varied retrieval, spacing and interleaving that I understood what was going on. Basically it's not so much the amount of times you retrieve something as the ways in which you retrieve it. So what we want is not so much rote repetition 3 times (although this has its place for certain things) so much as a kind of variation in how students retrieve knowledge. We want students to have to retrieve something in a range of different ways, across a range of different times and to apply it in a range of new ways. So when planning retrieval, the key things are: 1. Structuring learning so concepts are revisited through different activities and assessment types. 2. Ensuring retrieval occurs across distributed time intervals. 3. Creating opportunities for students to apply knowledge in novel contexts. 4. Designing assessments that require different forms of processing the same material. There is a broad consensus that varied retrieval practice enhances long-term retention significantly more than simple repetition or rereading. When students encounter material through different modalities and contexts, they develop multiple retrieval pathways to access that information.