Open any college textbook and you'll likely find pages covered in yellow, pink, blue, and green highlights. Walk into any library during exam season and you'll see students hunched over their books, markers in hand, carefully coloring line after line of text. Highlighting is one of the most popular study strategies in the world.
It's also one of the least effective.
In 2013, psychologist John Dunlosky and his colleagues published a landmark paper evaluating ten common study techniques based on the available research evidence. Their verdict on highlighting was blunt: highlighting and underlining received a "low utility" rating — the lowest possible category. The research consistently shows that highlighting produces minimal learning benefits and may actually harm comprehension in some cases.
If you're a dedicated highlighter, this might be hard to accept. But understanding why highlighting fails — and what to do instead — could be the single most impactful change you make to your study routine.
The Dunlosky Study: Rating Study Techniques
Before diving into highlighting specifically, it's worth understanding the broader context of Dunlosky's research.
John Dunlosky, Katherine Rawson, Elizabeth Marsh, Mitchell Nathan, and Daniel Willingham systematically reviewed the evidence for ten popular study techniques, evaluating each based on four criteria: generalizability across learning conditions, generalizability across student populations, generalizability across materials, and the strength of the evidence base.
The results challenged many common assumptions about studying.
High utility techniques (strong evidence of effectiveness): practice testing and distributed practice (spaced study).
Moderate utility techniques (promising evidence): elaborative interrogation, self-explanation, and interleaved practice.
Low utility techniques (minimal evidence of effectiveness): summarization, highlighting/underlining, keyword mnemonic, imagery for text, and rereading.
The fact that the two most popular study methods — highlighting and rereading — received the lowest ratings is a damning indictment of how most students study. And it raises an important question: if highlighting doesn't work, why does it feel like it does?
Why Highlighting Feels Effective
The Fluency Illusion
The primary reason highlighting feels effective is the fluency illusion — a cognitive bias where the ease of processing information is mistaken for genuine understanding.
When you highlight a passage and later review it, the highlighted text pops out at you. You recognize it instantly. This recognition creates a feeling of familiarity that your brain interprets as knowledge. "I highlighted this, I recognize it, therefore I know it."
But recognition and retrieval are fundamentally different cognitive processes. Recognizing highlighted text in your textbook (where the answer is right in front of you) tells you nothing about whether you could retrieve that information on an exam (where it's not). The fluency illusion tricks you into feeling prepared when you're actually not.
The Productivity Illusion
Highlighting also creates an illusion of productivity. Moving a marker across text feels like doing something. At the end of a study session, you can see the physical evidence of your work — brightly colored pages that testify to your effort. This visual feedback is satisfying and creates a sense of accomplishment.
But effort spent highlighting is not the same as effort spent learning. You can highlight an entire chapter without processing a single idea deeply enough to remember it. The hand moves, the page changes color, but the brain barely engages.
Selection Feels Like Comprehension
The act of choosing what to highlight requires some engagement with the text — you have to read it and make a judgment about what's important. This selection process creates the feeling that you're actively processing the material.
However, the level of processing required to identify "this seems important" is far shallower than the level required to understand, elaborate on, and encode information into long-term memory. Highlighting engages the shallowest level of processing, which produces the weakest memories.
Why Highlighting Actually Fails
Passive Engagement
The fundamental problem with highlighting is that it's a passive strategy. Your eyes move across the text, your hand moves across the page, but your brain isn't doing the deep cognitive work that creates durable memories.
Effective learning requires active processing — transforming information rather than just marking it. You need to explain concepts in your own words, connect new information to prior knowledge, generate examples, and test your understanding. Highlighting does none of these things.
No Generation Effect
Cognitive psychology has established that the generation effect — the finding that information you generate yourself is remembered better than information you passively receive — is one of the strongest memory phenomena.
When you highlight, you're not generating anything. You're selecting and marking text that someone else wrote. This produces no generation benefit. Compare this to writing a summary in your own words, creating flashcards, or teaching the concept to someone else — all of which require generation and produce stronger memories.
Over-Highlighting Negates the Purpose
In theory, highlighting could serve a useful organizational function — marking the most important information for later review. But in practice, most students highlight far too much. Studies consistently show that students highlight 30-50% or more of a text, essentially turning the highlighting exercise into a slightly more colorful version of rereading.
When everything is highlighted, nothing is. The supposed benefit of distinguishing important from unimportant information disappears when half the page is glowing yellow.
Potential for Harm
Some research suggests that highlighting may actually harm learning in certain situations. When students highlight specific facts, they may focus narrowly on those facts at the expense of understanding the broader conceptual structure. This can impair the ability to make inferences and connections — the higher-order thinking that exams increasingly test.
A study by Peterson found that students who highlighted performed worse on inference questions than students who simply read the text without highlighting. The highlighting may have directed attention toward isolated facts and away from the relationships between ideas.
What the Research Says You Should Do Instead
If highlighting doesn't work, what does? Dunlosky's research points to several alternatives with strong evidence bases.
Practice Testing (Active Recall)
Rated as high utility by Dunlosky, practice testing — also known as active recall or retrieval practice — is the strategy of testing yourself on material rather than reviewing it passively.
Instead of highlighting key terms in your biology textbook, close the book and try to write down everything you remember about the topic. Instead of rereading highlighted passages before an exam, use flashcards that force you to produce the answer from memory.
The mechanism is simple: retrieving information from memory strengthens the memory trace, making it more accessible in the future. Every successful retrieval makes the next retrieval easier. And even unsuccessful retrieval attempts — when you struggle but can't quite remember — still strengthen the memory when you subsequently review the correct answer.
Practice testing works across all ages, all materials, and all levels of complexity. It is, by a wide margin, the most effective study strategy available to students.
Distributed Practice (Spaced Study)
Also rated high utility, distributed practice involves spreading study sessions across time rather than concentrating them. Reviewing your biology notes three times over three weeks produces far stronger memories than reviewing them three times in one evening.
The spacing effect has been replicated in hundreds of studies and works because it allows for memory consolidation between sessions, provides practice retrieving information after a delay, and encodes information in multiple contexts, creating more retrieval pathways.
Elaborative Interrogation
Rated moderate utility, elaborative interrogation involves asking yourself "Why?" and "How?" questions about the material you're studying. Instead of highlighting "The mitochondria is the powerhouse of the cell," ask yourself: "Why is it called the powerhouse? How does it generate energy? Why do cells need this much energy?"
This strategy works because it forces deep processing — you have to connect new information to your existing knowledge and understand causal relationships, not just recognize isolated facts.
Self-Explanation
Also rated moderate utility, self-explanation involves explaining the material to yourself as you study. After reading a passage, pause and explain in your own words what it means, why it matters, and how it connects to other concepts.
This is essentially the generation effect in action: by producing your own explanation rather than passively absorbing someone else's, you create stronger, more interconnected memories.
Interleaved Practice
Rated moderate utility, interleaving involves mixing different topics or problem types during study sessions rather than studying one topic exhaustively before moving to the next. While this feels less organized and more difficult, it produces superior transfer and long-term retention because it forces you to discriminate between different types of problems and select appropriate strategies.
How to Break the Highlighting Habit
If you've been highlighting for years, switching to more effective strategies requires deliberate effort. Here's a practical transition plan.
Replace Highlighting with Questions
Instead of highlighting a key passage, write a question in the margin that the passage answers. This transforms a passive marking action into an active processing action and creates a built-in tool for self-testing during later review.
For example, instead of highlighting "Synaptic plasticity is the ability of synapses to strengthen or weaken over time," write in the margin: "What is synaptic plasticity, and why does it matter for learning?" Now when you review, you have a question to answer rather than highlighted text to reread.
Replace Highlighting with Summaries
After reading a section, close the book and write a brief summary in your own words. This requires understanding the material at a deeper level than highlighting does and engages the generation effect.
Your summary doesn't need to be perfect or polished. The learning value comes from the act of generating it, not from the product itself.
Replace Review-of-Highlights with Self-Testing
Instead of reviewing highlighted passages before an exam, create and use practice tests. Write questions based on the material, use flashcards, or work through practice problems. The effortful retrieval required by self-testing is what strengthens memory, not the passive recognition of previously highlighted text.
Use Highlighting Sparingly and Strategically
If you can't completely give up highlighting, use it sparingly and in combination with active strategies. Limit yourself to highlighting only the single most important sentence per section. Then, immediately after highlighting, close the book and explain why that sentence is important and how it connects to the broader topic.
This approach uses highlighting as a minimal organizational tool while ensuring that the heavy lifting of learning is done by active processing, not by coloring.
The Bigger Picture: Studying Should Feel Hard
The reason students gravitate toward highlighting and other passive strategies is that they're easy and comfortable. Reading and highlighting a textbook chapter feels smooth and productive. Self-testing, by contrast, feels frustrating and slow — you can't remember things, you get answers wrong, and progress feels uncertain.
But this difficulty is exactly the point. The strategies that feel hardest — active recall, spacing, interleaving — are the strategies that produce the strongest learning. The ease of highlighting is not a feature; it's a bug. If studying feels effortless, you're probably not learning much.
This concept, known as desirable difficulties, is one of the most important insights in learning science. Effective studying is supposed to be challenging. The struggle is the learning.
Conclusion
Highlighting is deeply ingrained in student culture, and abandoning it feels counterintuitive. But the evidence is unequivocal: highlighting produces minimal learning benefits, creates dangerous illusions of understanding, and diverts time and effort from strategies that actually work.
The alternatives — practice testing, spaced study, elaborative interrogation, self-explanation, and interleaved practice — require more cognitive effort. They feel harder, slower, and less productive in the moment. But they produce dramatically better learning outcomes that show up where it matters: on exams, in future courses, and in your long-term retention of knowledge.
Put down the highlighter. Pick up a blank sheet of paper and test yourself. That single change in study behavior, backed by decades of cognitive science research, may be the most impactful academic decision you make.