Gesturing is ubiquitous in communication and serves an important function for listeners, who are able to glean meaningful information from the gestures they see. But gesturing also functions for speakers, whose own gestures reduce demands on their working memory. Here we ask whether gesture's beneficial effects on working memory stem from its properties as a rhythmic movement, or as a vehicle for representing meaning. We asked speakers to remember letters while explaining their solutions to math problems and producing varying types of movements. Speakers recalled significantly more letters when producing movements that coordinated with the meaning of the accompanying speech, i.e., when gesturing, than when producing meaningless movements or no movement. The beneficial effects that accrue to speakers when gesturing thus seem to stem not merely from the fact that their hands are moving, but from the fact that their hands are moving in coordination with the content of speech. (Contains 1 table and 2 figures.)