Most people study by blocking — drilling one topic before the next. Interleaving mixes Most people study by blocking — drilling one topic before the next. Interleaving mixes related types up instead, and on delayed tests it reliably wins. Here’s what the evidence shows, why it feels worse than it is, the mechanism behind it, and the honest limits of where it works. types up instead, and on delayed tests it reliably wins. Here’s what the evidence shows, why it feels worse than it is, the mechanism behind it, and the honest limits of where it works.