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Hi Emily, do you have any good data on baby sign language and its impact on speech development? I find lots of opinions about it online — some that it delays speech and some that it improves speech — but not much data. It’s hard to believe no one has done a randomized controlled trial. (I’m asking specifically about children under age 2, i.e. not about its use in older children who are non-verbal.)
—Caitlin
It is hard to believe, but, no, there are no randomized controlled trials of this. I find that very surprising! Not so much because I think this is a medically crucial question, but just because it seems of significant interest to many parents. It seems like it might tell us something about baby language development.
In the absence of a randomized trial, we could imagine comparing children whose parents used sign language with them to those who did not. But because the use of baby sign language is associated with other characteristics (like parental education), these comparisons would not likely be causal.
This is a case where we know basically nothing despite enormously strong online claims. In looking into it, I found a paper whose abstract answered this question far better than I could. So I will defer to them, the authors of a paper entitled “Evidence for Website Claims about the Benefits of Teaching Sign Language to Infants and Toddlers with Normal Hearing.” Here is a (slightly condensed) version of their abstract:
Community GuidelinesA popular trend gaining national media attention is teaching sign language to babies with normal hearing whose parents also have normal hearing. Thirty-three websites were identified that advocate sign language for hearing children as a way of promoting better developmental outcomes. These sites make several claims about the positive benefits of teaching hearing infants and toddlers to sign, such as earlier communication, improved language development, increased IQ, reduced tantrums, higher self-esteem, and improved parent–child bonding. Without endorsing or disparaging these claims, the purpose of this article was to evaluate the strength of evidence cited on websites that promote products to teach young children to use sign language. Cumulatively, 82 pieces of evidence were cited by the websites as supporting research. However, over 90% of these citations were opinion articles without any supporting data or descriptions of products and only eight were empirical research studies relevant to the benefits of teaching sign language to young children with normal hearing. Unfortunately, there is not enough high-quality evidence cited on these websites to draw research-based conclusions about whether teaching sign language to young children with normal hearing results in better developmental outcomes.
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Another important consideration is that what hearing parents “teach” their hearing babies is often not American Sign Language, it’s some version of “Baby sign” which is not a real language. Use of baby sign instead of ASL is an appropriation of deaf culture for hearing parents without increasing the inclusive use of ASL by teaching a real language. I would imagine that – just like any other foreign language acquisition – that any real developmental benefits would come from bilingual acquisition of ASL and not just using a couple words here and there or using a made up language. I think of baby sign as something akin to making up words that “sound like” Spanish and calling it Spanish. Maybe that word means something to you and your child and you can use it to understand each other, but neither you nor your child are going to be able to use it to speak Spanish with someone.