Highlighting is the most popular revision activity among secondary students — and one of the least effective when used in isolation. Passively marking text produces minimal memory gains compared to techniques that require active retrieval. Highlighting can be genuinely useful, but only as part of a structured approach — the key is knowing when and how to use it.
Why does passive highlighting barely work?
Highlighting feels productive because your eyes move over the material and you make visible marks on the page. But this creates an illusion of learning — what psychologists call a "fluency illusion." Re-reading highlighted text feels easy and familiar, which the brain interprets as knowing the material. In reality, recognition (seeing something and feeling it is familiar) is far weaker than recall (retrieving something from memory without seeing it first).
The Dunlosky review of study techniques (2013) — one of the most cited studies in educational psychology — rated highlighting as low utility when used as a standalone revision method. It found that students who highlighted scored no better on subsequent tests than students who had simply read the text.
This does not mean highlighters are useless. It means highlighting needs to be combined with active strategies to become effective.
What is the difference between passive and active highlighting?
| Approach | What happens | Effect on memory |
|---|---|---|
| Passive — highlight while reading for the first time | You mark what seems important without testing yourself | Minimal — creates fluency illusion |
| Active — highlight after self-testing | You read, close the book, try to recall; then re-read and highlight only what you missed | Stronger — highlighting now marks genuine gaps |
| Selective and coded — use colours with meaning | Assign each colour a specific type of content; highlight sparingly | Moderate — forces prioritisation and categorisation |
The shift from passive to active highlighting is simple: do not highlight until you have first tried to recall the material without looking.
How do I use a colour-coding system that actually helps?
A colour-coding system only helps if it is consistent, limited to a small number of colours, and applied after thinking — not while reading passively. A practical three-colour system:
| Colour | Meaning |
|---|---|
| Yellow | Key term or definition |
| Green | Important fact, figure, or example |
| Pink/Orange | Something I don't fully understand yet — needs more work |
The pink/orange category is particularly powerful: it converts your highlighter into an error log. Any pink highlight in your revision notes means "come back to this." At the end of a study session, scan for pink highlights and address at least one before stopping.
Use highlighters sparingly. If more than 30% of a page is highlighted, you have not been selective — and a page that is mostly highlighted is just as hard to review as an unhighlighted one.
A worked example: the retrieve-then-highlight method
Step 1: Read a section of biology notes on the circulatory system (5 minutes).
Step 2: Close your notes. On a blank piece of paper, write down everything you can remember about the circulatory system — every term, every process, every structure (5 minutes).
Step 3: Reopen your notes. Compare what you wrote to the actual content. Everything you missed — the terms you couldn't recall, the facts that weren't on your paper — highlight in yellow.
Step 4: Those highlighted sections are your learning gaps. Spend the remainder of the session actively revisiting and re-testing those specific items.
In this method, the highlight marks your ignorance, not your recognition. That is fundamentally more useful.
What should I never highlight in revision notes?
Knowing what not to highlight is as important as knowing what to highlight:
- Do not highlight transition words ("however", "in addition", "furthermore") — these are structural words, not content.
- Do not highlight sentences in full. Highlight only the key term, the key number, or the key phrase — not the surrounding explanation. The explanation should come from your memory.
- Do not highlight things you already know well. The purpose of highlighting is to flag what needs attention, not to reward confidence.
- Do not highlight on a first pass through new material. Always read and attempt recall first.
Can highlighting help with revision planning as well as content?
Yes — one underused application of highlighting is at the planning stage. When reviewing your specification or a topic list before starting revision:
- Highlight topics you feel confident about in one colour.
- Highlight topics you feel uncertain about in another colour.
- Highlight topics you have not yet revised at all in a third colour.
This gives you a visual revision priority map that takes five minutes to create and is far more useful than a generic timetable. It also stops you from spending revision time on material you already know well — a very common inefficiency.
Frequently asked questions
Is it better to highlight my own notes or a printed revision guide?
Your own notes are more valuable to highlight because you wrote them actively, so they already represent your understanding. Highlighting a revision guide you did not write yourself is slightly closer to passive reading — you are processing someone else's summary. That said, a well-organised revision guide is perfectly valid to highlight with the retrieve-then-highlight method: attempt recall first, then highlight the gaps. Do not highlight anything you already know; reserve highlighter for information that genuinely surprised you by being absent from your recall attempt.
How many colours of highlighter should I use?
Three to four is the practical maximum for a consistent system. Beyond four colours, students typically forget what each colour means and the system collapses into random colour use. The system only works if every colour has a meaning you can apply consistently across all subjects. Some students use just two colours: "important" and "don't fully understand yet" — a simpler version that works well for students who find multi-colour systems hard to maintain.
My teacher highlights things in class — should I copy those highlights into my own notes?
Copying teacher highlights directly is slightly more active than passive reading, but it is still closer to copying than to recalling. A better approach: note what your teacher highlights (perhaps with a simple tick or asterisk in your own notes at the time), then after the lesson, attempt to recall what those items were before going back to mark them. If your teacher highlights frequently, their highlights are probably a reliable guide to what is most testable — treat those items as high-priority for flashcard or retrieval practice.
Does digital highlighting in revision apps work the same way?
Digital highlighting (in apps like Notability, GoodNotes, or PDFs on a tablet) works the same way as physical highlighting in terms of the underlying cognitive mechanism — passive highlighting is still passive whether it is digital or physical. The same rules apply: retrieve before highlighting, use colours with consistent meaning, and highlight sparingly. One advantage of digital highlighting is the ability to search for highlights across documents — this makes it easier to compile a revision list from your gaps across multiple topics.
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