Is Highlighting Effective? The Research and a Better Way

Is highlighting effective? Mostly no, at least the way most students do it. Highlighting helps you remember the specific lines you marked a little better than plain reading, but it rarely improves understanding, and in one study it hurt performance on questions that required inferences.

A major 2013 review of study techniques rated highlighting "low utility", alongside rereading. The good news is that the problem is how people highlight, not the pen itself. Marked sparingly and turned into questions, highlights can become a useful first step toward self-testing.

This post covers what the studies found, why highlighting usually fails, when it does help, and a method for turning highlights into questions you can actually recall.

Is highlighting effective? What the studies found

The best-known review is by John Dunlosky and colleagues in 2013. They looked at decades of experiments on highlighting and underlining (which work the same way) and concluded that, in most situations and with most learners, it "does little to boost performance."

A typical study gives a clear picture. In a 1974 experiment by Fowler and Barker, undergraduates had one hour to study about 8,000 words of articles from Scientific American and Science. One group just read. One group highlighted freely. A third read copies already highlighted by students in the second group. A week later, after 10 minutes of review, everyone took a 54-question multiple-choice test. The highlighting groups did no better than the readers.

The details explain why:

• Highlighters did better on questions about the lines they had marked.
• They did slightly worse on questions about lines they hadn't marked.
• The more they highlighted, the lower they tended to score (a correlation of −.29, though with only 19 students it wasn't statistically reliable).

A 2022 meta-analysis by Héctor Ponce, Richard Mayer, and Ester Méndez pooled 85 results from 36 published articles dating from 1938 to 2019. It found a modest memory benefit from students' own highlighting compared with reading alone, but no reliable benefit for comprehension.

Two more findings from that analysis matter for you. Students' own highlighting helped college students (0.39) but not school students (0.24, not reliable). And highlights chosen by an instructor helped both groups, which suggests the problem is usually choosing what to mark.

Why highlighting doesn't work for most students

You mark too much

Researchers explain highlighting's benefit with the isolation effect: something that stands out from its surroundings is easier to remember, like the word "cow" in a list of furniture. A highlighted line pops out of the page. But when half the page is yellow, nothing stands out, and you lose the one benefit highlighting offers.

You mark the wrong things

Picking the key sentence requires knowing the subject, which is exactly what a beginner lacks. In one study of airmen reading about aircraft engines, pre-underlined text helped those with high mechanical-aptitude scores more than those with low scores. If you don't know a subject yet, it's hard to tell a main idea from a detail, so everything looks worth marking.

It splits ideas into fragments

Highlighting draws your attention to individual sentences, not to how they connect. In a 1992 study by Peterson, education majors studied a 10,000-word history chapter. Students who underlined and then reviewed their marked copies did as well as readers on factual questions but worse on inference questions that required linking ideas across the chapter. Dunlosky's team called this perhaps the most concerning result in the literature, though it still needs replication.

It leads to rereading

The usual next step is to reread the highlights before the exam. That is passive review, and it has the same flaw as rereading the whole chapter: familiar text feels known, even when you couldn't produce it with the page closed. We explain that trap, and the research behind it, in active recall vs passive learning. In their review, Dunlosky's team noted that highlighting's biggest cost may be the time it takes away from techniques that work better.

When can highlighting help?

The research points to a few conditions where marking text does some good:

• Strict limits. In a 1975 study by Rickards and August, students allowed to underline just one sentence per paragraph recalled more of a science text than students who didn't underline.
• Training with feedback. Training students to find main ideas before marking, with feedback on practice texts, improved their results. Every training study included some guard against over-marking; in one, students lost points for underlining extra material.
• Harder texts and real effort. In one study, underlining helped more with a difficult version of a text than an easy one, and helped only when students were offered a $5 prize for top scores. That suggests many students can highlight well but usually don't.
• Good highlights from someone else. In a classroom study, students who received articles with five key statements underlined in red scored higher on exam questions about those statements. If your instructor or study guide flags what matters, use it.

How to highlight effectively

If you're going to highlight anyway, these rules turn it from decoration into preparation:

1. Read the whole paragraph first, pen down. You can't judge what matters until you've seen it all.
2. Mark one phrase, not a sentence. Aim for the few words that answer "what is this paragraph about?"
3. Write the question in the margin. Next to each highlight, write the question it answers. This is the step that makes highlighting useful.
4. Use one color. Sorting highlights into color categories is extra work that doesn't make you retrieve anything.
5. Review by covering, not rereading. Cover the page, read the margin question, answer it, then check.

The highlight-to-question method

Here is the method on a real paragraph. Say your economics textbook says:

Price elasticity of demand measures how much the quantity demanded responds to a change in price. Demand is elastic when the percentage change in quantity is larger than the percentage change in price, as with restaurant meals, which have many substitutes. Demand is inelastic when quantity barely changes, as with insulin. Raising the price of a good with inelastic demand increases total revenue; raising the price of a good with elastic demand reduces it.

Typical highlighting: nearly every line goes yellow. Later you reread it, it all looks familiar, and you move on.

The method: read it once, then mark two phrases: "percentage change in quantity is larger than the percentage change in price" and "inelastic demand increases total revenue". Then write these in the margin:

• What makes demand elastic rather than inelastic?
• Why is demand for restaurant meals elastic?
• A drugmaker raises the price of insulin by 10%. What happens to its revenue, and why?
• Name a good with elastic demand that isn't in the textbook.

The last two questions go beyond what's on the page. They make you apply the idea, which is exactly what plain highlighting doesn't do. Use this table to write questions from any kind of highlight:

Questions like these are the start of active recall. To practice them on a schedule, move them into flashcards. Our notes to flashcards workflow shows how, and the Cornell note-taking system builds the margin-question habit into your notes.

A 15-minute routine for one textbook section

1. Preview (1 minute). Turn each heading into a question and guess the answer, a quick form of pretesting. "Price elasticity" becomes "What is price elasticity and why does it matter?"
2. Read (6 minutes). One paragraph at a time, pen down.
3. Mark and ask (3 minutes). One phrase per paragraph, one margin question each.
4. Cover and answer (4 minutes). Cover the text and answer every margin question aloud or on paper.
5. Flag misses (1 minute). Put a dot next to any question you got wrong. Those come back tomorrow.

The next day, answer the dotted questions first, without rereading. If you'd rather not write every question by hand, you can upload the chapter PDF to a PDF-to-flashcards tool to draft cards, then edit anything vague.

For more ways to make reading stick, see how to remember what you read and the SQ3R reading method, which builds questions in before you start reading.