What is Highlighting?
Highlighting is marking selected text while reading to flag what matters. Used alone, it is weak: the landmark Dunlosky review rated mark-and-reread low utility for learning. Used selectively as a capture step that feeds recall, notes, and spaced review, it becomes the front door to techniques that do work.
The evidence deserves honest framing. In Dunlosky and colleagues' review of ten study techniques, highlighting and underlining received the lowest rating, low utility: when students simply mark text and reread the marks, they learn little more than from plain reading, and marking can even hurt performance on inference questions. Benefits appeared mainly when marking was selective, because deciding what matters is where the cognitive work happens.
The rating's scope is narrower than the headline. The underlying studies tested highlighting as a one-pass, standalone activity followed by rereading. They did not test highlighting as the capture step of a larger system, where marked passages become prompts for retrieval practice, material for notes in your own words, or items in a spaced review queue. That workflow is largely untested rather than debunked.
The practical guidance follows directly: highlight sparingly, since marking whole paragraphs skips the selection judgment that provides the benefit, and treat every highlight as a promise of a second action. A highlight that later becomes a recall prompt, an annotation, or part of a summary has done its job; a highlight that is only ever reread has not.