Is highlighting your notes actually useful?

Dunlosky, Rawson, Marsh, Nathan and Willingham compared ten study techniques. Two received a high utility rating, practice testing and spreading out your study. Three received a moderate rating. Five received a low rating, including summarizing, rereading and highlighting or underlining (Dunlosky et al., 2013).

The word low has a precise meaning. It means the available evidence does not show a benefit solid enough or general enough to recommend the technique, whereas other methods did show one. It does not mean highlighting wastes time every single time. Once that frame is set, a useful question becomes the opportunity cost. An hour spent highlighting a biology chapter is an hour you do not spend quizzing yourself on it. The full table of the ten techniques is in How to study effectively, according to the research, with the rating of each.

Highlighting feels like work. The page fills with color, you move forward, you feel like you are sorting out what matters. But the gesture is mostly a reading activity, not a recall activity. You have nothing to retrieve from memory, you are going over what is already in front of you.

The authors of a survey of 177 students found that most reread their notes or textbook, and relatively few quiz themselves, and they speak of an illusion of competence (Karpicke et al., 2009). That survey was not specifically about highlighters, but it describes the same mechanism, passive methods that give confidence. In the study by Roediger and Karpicke, the students who reread were the most confident they would remember, and they are the ones who had forgotten the most a week later (Roediger and Karpicke, 2006). Bjork and colleagues describe this gap between the feeling of mastery and actual memory (Bjork et al., 2013). When a course is all yellow, it looks known. That does not prove it is.

What follows is practical advice, not a study result. If you like highlighting, use it as a marking tool and not as a memorization method. Highlight little, one sentence or one word per paragraph, then close the course.

Next, turn each colored passage into a question. If you highlighted the date the Treaty of Versailles was signed in your history course, write “When was the Treaty of Versailles signed?” on a card, and answer it the next day without looking. Highlighting with no question behind it remains rereading in disguise. With the question, it becomes the starting point of the top-rated technique, practice testing (Dunlosky et al., 2013). You can also run those questions through cards, see How to make flashcards that actually work. The highlighter then serves as a marking pencil, and it is the question that does the memory work.

In experiment 2 by Roediger and Karpicke, reading once then quizzing three times gave 61% of ideas remembered after a week, against 40% for four rereadings (Roediger and Karpicke, 2006). The gap is not about the highlighter itself, but it shows where most of the benefit lies, in the effort of recalling.

Active recall also produced more learning than elaborate study with concept maps (Karpicke and Blunt, 2011). To get organized, the page Active recall, why quizzing yourself beats rereading explains the method and Why rereading your notes is not enough covers the rereading trap. In high school as in college, a good rhythm is to read the chapter once, mark three or four ideas, write questions on them, then ask them on spaced days. For a midterm in 10 days, for example, the first review of your questions falls 2 to 4 days after the first session (Cepeda et al., 2008).