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Do you have any good data on baby sign language and its impact on speech development? I find lots of opinions about it online — it either delays speech or 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. The gist is that while many websites make sweeping claims about the benefits of teaching sign language to hearing babies, when researchers examined the evidence behind them, the results were underwhelming.
Of 82 references cited across these sites, most were opinion pieces or product descriptions rather than real data. Only a few solid studies exist, and they don’t show clear developmental advantages. In other words: baby sign language isn’t harmful — and it might be a fun way to connect — but there’s not enough high-quality evidence to suggest it gives kids a measurable boost.
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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.