Hi K.,
We signed with our son and he is very advanced in his verbal communication. By his 2nd birthday he was speaking in 6-7 word sentances linked into paragraphs. Everyone is amazed with his speaking. We loved signing with him and it completely eliminated his frustrations around the 1 year mark. We started at birth with him and he was signing by 6 months.
Keep researching...there are a lot of studies that will show you the benefits of signing with hearing children.
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In 1987, Garcia began to research the use of Amercian Sign Language with hearing babies who are exposed to signs regularly and consistently at six to seven months of age can begin expressive communication by their eighth or ninth month.
Drs. Linda acredolo and Susan Goodwyn conducted a longitudinal study funded by the National Institutes of Child Health and Human Development. The study showed that signing babies understood more words, had larger vocabularies and engaged in more sophisticated play than non-signing babies. Parents of the signing babies in the study noted decreased frustration, increased communication, and enriched parent-infant bonding. Signing babies also displayed an increased interest in books (Moore et al, 2001).
They revisited the families in the original study when the children were seven and eight years old. The children who signed as babies had a mean IQ of 114 compared to the non-signing control group's mean of 102 (Acredolo and Goodwyn, 2000).