Studies consistently show that children from higher socioeconomic brackets have, on average, bigger vocabularies than those from lower-income families. The trend starts in the toddler years and grows until kids enter school. The reasons for the disparity are many, but recent research has suggested that one contributing factor may be how we use our hands, not just our words.

Meredith Rowe, an expert on language and gestures from the University of Maryland, studied 50 children starting at age 14 months and continuing through to 54 months. Without instructing them at all, the scientists videotaped the families’ natural routines during 90-minute sessions. The interactions were then coded, with special attention paid to non-verbal communication on the part of mom, dad, and baby.

At 14 months, all the toddlers in the study had fairly equal vocabularies, but both the children and parents from higher-income families used their hands to communicate more. By the time the children were four and a half, the gap had widened, with those from more well-off households having significantly bigger vocabularies. The researchers aren’t sure why moms and dads from higher-income families had extra-active hands, but it appears that the children had learned this behavior early on, and it gave them a head start on spoken words.

Why would hand movements give a boost to kids’ verbal skills? The scientists say that when a baby is able to gesture (usually starting around 10 months), it allows parents to tailor their responses specifically to the child’s cues, so the more gesturing the baby does, the more opportunities there are for learning. This makes sense – if we know what’s going on in our kids’ little heads, we can label it, talk about it, and expand on it with them.

But it’s also possible that the act of a baby moving his hands actually solidifies knowledge. Hearing the word “kiss” is important, but coupling it with baby and mom blowing kisses to each other helps the brain code the language more clearly.

The relationship between income and vocabulary is complex, and gesturing is clearly one of many forces at play. We don’t know for sure that gesturing causes the growth in words, although the researchers suspect this is the case. It has also been shown (in this study and others) that children in higher-income households hear more spoken words as well, so it’s hard to tease apart the influence of verbal and non-verbal communication. In this study, however, the uptick in hand signals came first, suggesting that they do play a role.

So maybe the proponents of baby sign are on to something. After all, what better way to incorporate gestures into your family interactions? But for those of us who aren’t up for the task of teaching formal sign language to our kids in the first year, it’s still important to think about how we express ourselves: pointing and making eye contact before we label something, throwing our arms up in the air when we say we’re excited, or motioning to ourselves and our babies while we’re taking turns. We always hear that we should talk, talk, talk, but it helps to remember that talking is more than just using our words.