Mix several kinds of problems when you practice, instead of doing twenty of one kind in a row

Moderate value
Evidence A
Saves time
Free
Takes minutes
Some willpower

In plain words

Doing a long string of the same type of problem goes smoothly at the time, but afterward you may not be able to tell which method to use. Practicing several types mixed together works better in the long run, by a medium amount. But it depends on the material: it works best for learning to recognize images and categories, a bit less for math problems, and for memorizing vocabulary, practicing in blocks is actually better.

Cost: Free. Change the workbook from doing problems in order of type to doing them mixed up. The hard part is that your accuracy is lower on the spot when you mix, and it feels like going backward.
What you get: A multilevel meta-analysis of 59 studies, 238 effect sizes and 158 samples. The overall effect of interleaved practice compared with blocked practice was medium (Hedges' g = 0.42). By material: painting categories did best (g = 0.67), other visual material also did well; the effect for math tasks was smaller (g = 0.34); the overall effect for expository text and for taste material was not significant; for vocabulary, blocked practice was better (g = −0.39). A regression showed that the more similar the categories are to each other, the less alike the items within a category are, and the more complex the material, the greater the benefit of interleaving.
Notes: The review cited in §23.16 (don't make highlighting your main way to study) rated interleaved practice in the middle tier, because at the time there was not enough research. Taken together, the use is: mix up content where you need to recognize “which kind this is and which method applies,” such as types of math problems, patient cases and applying statutes; practice in blocks content that has to be memorized outright, such as vocabulary and definitions.
Evidence grade: A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.
Sources: Brunmair M, Richter T (2019). Similarity matters: A meta-analysis of interleaved learning and its moderators. Psychological Bulletin, 145(11), 1029–1052. https://doi.org/10.1037/bul0000209

Translated from the Chinese original. Original book, section 23, tip 17. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer