Mix practice when choosing the method is part of the skill
Practising one problem type repeatedly can tell you which method to use before you even read the question. Mixing related types requires you to identify the method yourself. Interleaving is especially relevant when the learning goal includes distinguishing between similar-looking situations.
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Practise the choice as well as the procedure
A page containing only triangle-area questions gives away the method. A mixed set containing several shapes requires you to decide which formula fits each one.
Interleaving mixes related categories or problem types during practice. It can help learners practise telling them apart, rather than merely repeating a procedure selected by the worksheet's heading.
This does not mean every subject should be mixed randomly from the start. A learner may first need enough instruction to understand the individual methods.
A note collection can support mixed practice by bringing together concepts that are easy to confuse. The useful challenge is identifying the relevant difference, not switching between unrelated subjects simply to make the session feel varied.