Does Highlighting Help You Learn?

In 2013 a team led by John Dunlosky reviewed the evidence for ten common study techniques and rated highlighting and underlining as "low utility". That finding is often quoted as "highlighting does not work", which is not quite what the review said. It said that highlighting, as most students do it, adds little to plain reading, and that in some conditions it can hurt. It also pointed at what helps. This article lays out both, because the conclusion for a reader is not "stop highlighting" but "highlight differently and then do something with it".

What the research actually found

• Highlighting alone barely beats reading. Across studies going back to the 1970s, students who highlighted while reading recalled about as much as students who simply read. The act of marking is not the act of learning.
• Too much highlighting can hurt. When students marked a large share of the text, they did worse on tests requiring inference than students who read without marking. Heavy marking flattens the text; nothing stands out, and attention to connections drops.
• Marked material is remembered at the expense of unmarked material. Highlighting focuses later attention on the marked lines, so if the highlights are poorly chosen, the wrong things are learned. This is the "isolation effect": marked items become more memorable partly because everything else becomes less so.
• Careful selection helps. In studies where students were trained to highlight selectively, or where the marking was done by someone who knew the material, later recall of the marked points improved. The benefit comes from the quality of the selection, not the presence of colour.
• Highlights help when they are used again. Reviewing highlighted material, especially by trying to recall it before rereading, produces the gains that highlighting on its own does not.

Why marking feels productive and is not

Highlighting produces a feeling of engagement. Your hand moves, the page changes, the passage looks important. But memory researchers distinguish between processing that is fluent (easy, feels like learning) and processing that is effortful (harder, actually builds memory). Highlighting is fluent. It does not require you to understand the passage, restate it, connect it to anything or retrieve it later. Those are the effortful acts that the strongest techniques, practice testing and spaced review, are built from. A highlight is at best a bookmark for effortful work to be done later, and most highlights are never visited again.

The conditions under which highlighting helps

A routine that makes highlights work

1. Read a section to the end without marking.
2. Go back and mark selectively using a simple colour code: the point in yellow, the proof in green, terms in pink.
3. Close the book or tab and write, from memory, one sentence per yellow mark. Then open it and correct yourself.
4. The next day, read only your sentences and try to recall the evidence for each. Check against the green marks.
5. Turn pink marks into flashcards or a two-column list and test yourself on them at increasing intervals.
6. Before an exam or a piece of writing, work from your notes, not the highlights. The highlights were scaffolding.

Steps 3 to 5 are practice testing and distributed practice, the two techniques Dunlosky's review rated as high utility. Highlighting's real job is to make those steps quick to set up. Our guide on turning highlights into notes gives a worked example.

Does highlighting help you study? A worked example

Take a short paragraph on a neutral subject, written for this page, and follow two readers through it. Both own a yellow highlighter. Only one of them learns anything that lasts.

Trees in temperate climates add one growth ring each year, and the width of the ring records the growing conditions. A wide ring means a warm, wet season when the tree grew quickly; a narrow ring means drought, cold or damage. Because trees in the same region respond to the same weather, their ring patterns match, and a scientist can line up the rings of a living tree with those of an old beam and date the beam to the year it was felled. This method is called dendrochronology.

The passive reader is not lazy; they are doing what the page invites. The selective reader has spent perhaps four more minutes and has done two things the research rewards: they chose, and they retrieved. The marks themselves were only the scaffolding for those two acts.

Does any of this change on a screen?

Not the psychology. Digital highlighting is as passive as the paper kind and easier to overdo because it is effortless to undo. Two things do change. Digital highlights can be exported and collected, which makes the retrieval routine easier to run across many sources. And digital highlights can be shared as links, which turns a private mark into a pointer for someone else; that is a communication act, not a study act, and it is what the highlight link tool on this site is for. Use the right kind for the job.

Pitfalls and expert tips

• Highlighting to stay awake. Marking gives the hand something to do during a dull chapter. It keeps you reading; it does not make you remember. If you notice your marks climbing, stop and write one sentence about the section instead.
• Treating a marked book as a revised book. A yellow chapter is a chapter you have read once. Revision is the recall work, and it has not started.
• Marking definitions in full. A whole sentence in pink hides the term you need. Mark the word and write the definition in your own phrasing in the margin.
• Undo makes it worse on screen. Because a digital highlight costs nothing, readers mark more of a PDF than of a paper page. Set yourself the paper ceiling anyway: about one line per paragraph.
• Never exporting. Highlights that stay inside a reading app are rarely revisited. Export them into a notes file you open again; exporting highlights into a file you can revise from explains where each app puts them.

Three tips from the research

• Mark after, not during. Read the section to its end, then decide which line carries it. This one habit removes most over-marking.
• Turn every yellow mark into a question the same day. "What does ring width record?" is a study tool; the highlighted sentence is not.
• Space the recall. A day, then a week, then a month. The intervals do more for memory than any amount of rereading between them.

For teachers

Students highlight because nobody has shown them anything better and because it feels like work. Teaching the routine above, especially the read-first-then-mark habit and the write-from-memory step, is one of the highest-return study skills lessons available, and it takes one class period. See highlighting for teachers for activities.

The practical follow-ups to this evidence are elsewhere in our pages on studying with highlights: a three-colour code for textbooks and PDFs puts selective marking into practice, and turning marks into study notes covers the retrieval step that makes highlights worth making.