At school, highlighting and underlining were ordinary parts of studying. We read a lesson, marked a few lines, and returned to them before an examination. I think about that habit now, when so much reading arrives as an uninterrupted stream of documents, articles and messages. Somewhere along the way, I began to expect myself to absorb larger amounts simply by keeping my eyes moving.
As I have grown older, I have sometimes treated that school habit as something I should no longer need. Yet familiarity with a subject can make me hurry. I want to take a step back and recover a small discipline: decide what matters before moving on. A highlighter gives that decision a visible form.
What does the evidence actually support?
A 2022 meta-analysis by Ponce, Mayer and Méndez brought together 36 articles. Learners making their own highlights showed a benefit for memory, but the pooled comprehension benefit was not statistically significant. Highlights supplied to learners showed benefits for both outcomes. My reading of this is cautious: highlighting can help, but comprehension is not guaranteed. Choosing useful material and understanding it remain separate jobs.
A 2024 study by Mason and colleagues compared three randomly assigned reading conditions, with 170 students completing both immediate and delayed tests. It found no overall learning advantage from the highlighting conditions. Better-quality highlighting was associated with better understanding of stated information and application of knowledge, but this association does not establish cause and effect. It encourages me to pay attention to what I select, without treating the amount of colour on a page as evidence that I have learned it.
How much of a paragraph would I mark?
The studies linked here do not establish a universally optimal number of phrases or percentage of a paragraph to highlight. An earlier experiment by Rickards and August tested instructions involving one underlined sentence per paragraph; a tested instruction is not a rule for every text. I would therefore avoid presenting “highlight exactly 10%” or “always mark two sentences” as a research requirement.
My own starting rule is one short phrase that carries the main idea. I would add a second only when an essential qualification or contrast would otherwise disappear. Some paragraphs need no highlight at all. This is a personal constraint to make me choose, not a scientifically established optimum. If the whole paragraph feels indispensable, I would finish reading it and try to summarise it before reaching for the colour.
Choose the meaning, not the impressive words
I begin with the reason I am reading. Am I trying to understand a concept, compare two explanations, or carry out an action? Depending on that purpose, the useful phrase may be a central claim, a definition, a contrast, a consequence or the next step. A technical term by itself may tell me the topic while leaving out the actual point. I want the marked words to answer the question the paragraph is addressing.
I also want to protect the small words. “Not,” “only” and “unless” can change a sentence completely. So can a limitation on whom a finding applies to. If a highlight drops that condition, it can turn a careful statement into a misleading one. Keep the qualification attached, even if that makes the selected phrase a little longer.
A small example
Here is an invented paragraph about an everyday decision. I have marked the action and the condition that controls it:
A neighbourhood reading group usually meets in the garden on Sunday morning. If rain is forecast, members should move the meeting indoors only after confirming the room is available. The organiser will then send everyone the revised location.
For someone arranging the meeting, the garden and the day provide context; the conditional action deserves attention. Highlighting only “move the meeting indoors” would lose an essential check. Another reader, looking for when the group meets, might select different words. The example reminds me that importance depends partly on the reading task, as well as on the structure of the paragraph.
Close the page for a moment
After choosing a phrase, I want to look away and explain the point in my own words. Roediger and Karpicke’s 2006 experiments found that retrieving studied material produced better delayed retention than repeated study. Those experiments were not a test of my highlighting routine. They give me a reason to add a brief recall check instead of ending the exercise at the coloured line.
Can I explain the idea without looking? Can I name the condition that limits it? If not, I need to return to the surrounding paragraph. Later, the highlight can act as a prompt: try to recall the point, then check it against the full text. I can also remove a mark that looked important initially but no longer helps.
I am not expecting a coloured phrase to make every long document quick or easy. I want a more deliberate encounter with what I read. The school habit is worth revisiting with that modest aim: read, choose, explain, return. A little colour can remind me where I paused long enough to think.
Studies behind this reflection
Ponce, Mayer and Méndez (2022) — a meta-analysis of learner-generated and instructor-provided highlighting.
Mason and colleagues (2024) — a study of highlighting conditions, selection quality and learning outcomes.
Rickards and August (1975) — an experiment on generative underlining and prose recall.
Roediger and Karpicke (2006) — experiments comparing retrieval practice and repeated study.
These are my own reflections and practical preferences, informed by the studies above.
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