No. Baby sign language does not delay speech development. This is one of the most persistent myths about introducing sign language to hearing children, but decades of research conclusively refute it. The American Speech-Language-Hearing Association (ASHA) states clearly: “Contrary to predictions often cited in the literature, acquisition of sign language does not harm spoken vocabulary acquisition.” Study after study across more than two decades confirms that children exposed to both sign and spoken language develop spoken language on a typical timeline—often with the added advantage of being able to communicate earlier through sign.
For example, a hearing baby with deaf parents who uses American Sign Language (ASL) will acquire their first signs at an earlier age than their peers acquire their first words. That same child will then develop spoken language normally, often through exposure to spoken language from extended family, childcare providers, or media. The combination creates a bilingual advantage, not a deficit. This article explores the research behind why this myth persists, how bilingual sign-language users actually develop language, and what the science tells us about early communication and cognitive development.
Table of Contents
- What Does the Research Actually Show About Sign Language and Speech Development?
- How Do Bilingual Children Actually Develop Language?
- Do Babies Actually Communicate Earlier with Sign Language?
- What Does Bilingual Language Development Look Like?
- What About Developmental Milestones and Cognitive Development?
- When Do Children Naturally Transition from Signing to Speaking?
- Why Does This Myth Persist?
- Conclusion
What Does the Research Actually Show About Sign Language and Speech Development?
The myth that sign language delays speech likely originated in outdated theories from the mid-20th century when bilingualism itself was misunderstood. Parents and professionals feared that exposing children to two languages would confuse them or slow down their development. We now know this was wrong. A systematic review of studies examining the relationship between sign language and spoken language acquisition found that all studies claiming a negative relationship had poor methodological quality. The higher-quality research consistently shows no delay.
The evidence is particularly strong for deaf children of deaf parents who use ASL as their primary language and then learn English later. These bilingual children develop total vocabularies—combining ASL and English—that are equivalent to same-age hearing monolingual children. Importantly, the size of a child’s ASL vocabulary positively correlates with their spoken English vocabulary. This suggests that the underlying language development systems are working normally, and learning sign language actually supports the development of other languages rather than competing with them. For hearing children raised in households where both sign language and spoken language are present, the advantage is even clearer. These children benefit from exposure to more language input overall, not less.
How Do Bilingual Children Actually Develop Language?
When a child is exposed to sign language and spoken language simultaneously, they don’t divide their language capacity in half. Instead, they build a unified language system where both languages feed into the same cognitive infrastructure for communication, grammar, vocabulary, and conceptual understanding. Research from the University of Connecticut shows that deaf infants exposed to sign language hit all the same developmental milestones as hearing children—they produce sign-phonetic and syllabic babbling on their hands, just as hearing babies produce sound babbling. The babbling looks different, but it serves the same developmental function.
However, it’s important to note that outcomes depend heavily on consistent, quality exposure to both languages. A child needs adequate input in both sign and spoken language to thrive bilingually. If a hearing child is exposed only to sign language and has minimal access to spoken language, they won’t naturally develop strong spoken language skills—not because sign language interferes, but because they simply weren’t exposed to enough spoken input. The reverse is also true: deaf children need sufficient exposure to sign language to develop strong sign language skills. Bilingual language development works best when both languages are present as meaningful, usable communication tools in the child’s environment.
Do Babies Actually Communicate Earlier with Sign Language?
Yes. One of the clearest advantages of introducing sign language early is that babies can communicate through sign at a younger age than through spoken words. Typical children as young as nine months can communicate through sign language—three months earlier than children relying solely on spoken language. This early communication window is significant because it allows babies to express needs, emotions, and interests before they have the motor control and cognitive ability to produce clear speech sounds.
For hearing families teaching baby sign language, this translates to a period where a prelingual child can actually have functional two-way communication. A nine-month-old baby who knows signs for “more,” “milk,” “all done,” and “up” can request things and convey basic wants. That same baby wouldn’t reliably say these words aloud until around 12 months or later. The ability to communicate earlier through sign language reduces frustration for both baby and parents and provides a natural bridge to later spoken language development. Importantly, this early signing does not replace the drive to speak—it simply provides an additional tool during the period before clear speech emerges.
What Does Bilingual Language Development Look Like?
Bilingual children develop language through what researchers call a “unitary language system”—one underlying conceptual framework that both languages access. A bilingual child’s vocabulary is best measured by combining the two languages, not by counting each separately. When research compares ASL-English bilingual deaf children to hearing monolingual children using total vocabulary (ASL words plus English words combined), the bilingual children show equivalent vocabulary sizes. This is crucial because it shows that bilingual children aren’t behind; they’re simply distributing their vocabulary across two language systems.
One practical consequence: a bilingual child might know the sign for “apple” and the spoken word for “apple,” or they might know the sign and the written word. When you combine their total vocabulary across both languages, they have learned just as much as a monolingual peer. However, if you measure only the child’s English vocabulary in isolation (ignoring their ASL vocabulary), it might appear lower than a monolingual child’s. This was the source of confusion in older research—researchers were measuring only one language and concluding the child was delayed, when in fact the child was simply bilingual. Understanding this distinction changes the entire interpretation of outcomes.
What About Developmental Milestones and Cognitive Development?
Deaf infants exposed to sign language reach all the expected developmental milestones at the same ages as hearing children. They babble on their hands. They progress from single signs to two-sign combinations. They begin to understand grammar and word order. They develop phonological awareness appropriate to their language—sign phonology rather than sound phonology, but equally sophisticated.
Their cognitive development proceeds normally because language development and cognitive development are intertwined. A child learning sign language isn’t experiencing language deprivation or developmental delay; they’re simply experiencing language in a different modality. One important caveat: these positive outcomes depend on early and consistent exposure to a natural language in either visual modality (sign) or auditory modality (spoken), or ideally both. Deaf children who do not receive exposure to sign language during the critical early years and who do not have access to effective spoken language through hearing aids or cochlear implants may experience delays in language development—not because sign language would delay them, but because they didn’t receive adequate language exposure in any modality. The absence of language input, not the presence of sign language, is what causes concern.
When Do Children Naturally Transition from Signing to Speaking?
Most children naturally progress from signing to speaking as their brains develop and as they gain more exposure to spoken language. Children who grow up in sign-rich, speech-rich environments don’t need to choose one language over the other; they become bilingual. For hearing children born to deaf parents who sign fluently, the natural progression depends on the broader language environment. If the child also has regular exposure to spoken language from other family members, teachers, peers, or media, they’ll naturally pick up spoken language and become bilingually fluent in both sign and speech.
In some cases, the signing gradually falls away as speech takes off around 18 months for typically developing children with more prominent speech exposure. In other cases, the child maintains fluency in both languages throughout childhood and into adulthood. There’s no automatic progression from sign to speech; rather, children use what works in their immediate environment and for their communicative needs. A hearing child of deaf parents who is fully bilingual in ASL and English remains fluent in both, not because of exceptional effort, but because bilingualism is their natural language environment.
Why Does This Myth Persist?
The myth about sign language delaying speech persists partly for historical reasons and partly because of misunderstanding how bilingualism works. In earlier decades, bilingualism itself was seen as a disadvantage—parents were told to choose one language. This outdated perspective influenced thinking about sign language and speech. Additionally, when researchers measured only English vocabulary in deaf children using sign language, they saw lower numbers and concluded delay without accounting for the child’s ASL vocabulary or the underlying bilingual capacity.
Today’s research is clearer and more methodologically sound, yet the myth endures in popular culture and among some professionals. Parents considering introducing sign language to their hearing children should know that the concern about speech delay is not supported by evidence. The legitimate concerns are different: ensuring that children have consistent access to quality instruction in sign language and that they also have adequate exposure to spoken language if speech development is a family goal. The combination is advantageous, not compromised.
Conclusion
The evidence is unambiguous: introducing baby sign language does not delay speech development. In fact, research shows that children exposed to sign language communicate earlier through signing, develop typical cognitive and language milestones on schedule, and show bilingual advantages that extend across languages. Families who raise their children bilingually in sign and spoken language are not compromising their children’s speech development—they’re expanding their children’s communicative and cognitive capacity.
The myth about delay is a remnant of outdated thinking about bilingualism and language. If you’re considering introducing sign language to your hearing child, the benefits are clear, and the concerns about speech delay have no scientific basis. The real focus should be on ensuring consistent, quality exposure to both sign language and spoken language, whatever languages are present in your family environment. Your child’s brain is capable of learning multiple languages simultaneously, and research confirms this leads to richer language development, not impoverished speech.