They said babies with wealthier, better-educated parents tend to gesture more and this may help explain why some children from low-income families fare less well in school.

"When children enter school, there is a large socioeconomic gap in their vocabularies," said the University of Chicago's Meredith Rowe, whose study appears in the journal Science.

Gestures could help explain the difference, Rowe told the American Association for the Advancement of Science annual meeting in Chicago.

Vocabulary is a key predictor of school success. Earlier research showed that well-off, educated parents tend to talk to their children more than their poorer, less-educated peers.

"What we are doing here is going one step earlier and asking, does this socioeconomic status relate to gesture, and can that explain some of the gap we see at school entry," Rowe said.

The researchers filmed 50 Chicago-area children and parents from diverse economic backgrounds and counted the number of gestures, such as pointing at a picture.

The team found that 14-month-olds from high-income, well-educated families used gesture to convey an average of 24 different meanings during each 90-minute session, compared with 13 meanings conveyed by children from lower-income families.

When the same children entered school at age four and a half, those from higher-income families had better vocabulary scores on standardized tests.

"At 14 months, an age when there aren't even socioeconomic differences in their talk yet, we see there are differences in their gestures," Rowe said.

The videos revealed that parents from wealthier families gestured more with their children than the other parents.

Rowe said the findings suggest that gestures can at least partly explain vocabulary differences between the groups, and may prove useful as the basis for interventions.