In a 2013 review published in Psychological Science in the Public Interest, researchers Dunlosky, Rawson, Marsh, Nathan, and Willingham evaluated the evidence behind ten of the most common study techniques students use. Highlighting and underlining — probably the single most common study behavior in the world — came in near the bottom, rated as having low utility.
Why highlighting feels so good
Highlighting is easy, fast, and gives you something to show for your effort: a textbook full of neon streaks that looks like evidence of hard work. That's part of the problem. The physical act of dragging a highlighter across a sentence requires almost no cognitive effort — you don't have to understand the sentence, summarize it, or connect it to anything else. You just have to decide it looks important.
That low effort is exactly why it doesn't build durable memory. Learning techniques that work tend to require some kind of active processing — retrieving, explaining, connecting ideas together. Highlighting asks almost nothing of your brain beyond a quick relevance judgment.
What the research actually found
Across the studies reviewed, highlighting showed little to no benefit over simply reading the text with no highlighting at all. In some experiments, heavy highlighters performed worse on later tests, possibly because highlighting can narrow attention to isolated facts and away from the connections between ideas that actually get tested.
It's worth being precise about what the research does and doesn't say. Highlighting isn't harmful in the sense of erasing knowledge — it's just a weak use of study time compared to the alternatives. The opportunity cost is the real issue: every minute spent color-coding a textbook is a minute not spent doing something with a much better return, like a practice test.
The problem with highlighting isn't that it's wrong. It's that it's the easiest thing to do with a textbook, and easy is usually a warning sign in learning, not a green light.
What actually works instead
The same review ranked two techniques as having the highest utility across age groups, subjects, and conditions: practice testing (retrieval practice / active recall) and distributed practice (spacing study sessions out over time instead of massing them together). Both require more effort than highlighting. Both also produce measurably better results, and the gap tends to widen the longer you wait before the test.
- Instead of highlighting a passage, close the book and write down what it said, in your own words.
- Instead of re-reading a highlighted section, quiz yourself on it a few days later.
- If you want to mark up a text, annotate with questions instead of highlights — "why does this matter?" does more cognitive work than a yellow stripe.
This is the underlying reason Ayanam Learn's daily capture step never asks you to copy or highlight anything from your notes. It asks you to recall, because recall is the technique with the evidence behind it.