Research indicates that a gap in language, gesturing, and other developmental markers begins to open by age 2, Ferguson says — even though there are virtually no racial or social class differences in the mental abilities of infants before age 1. (gse.harvard.edu)
Drawing from an experienced set of experts in a range of fields, including CASEL's Roger Weissberg, this website provides developmental markers at each age / stage, with guidance for parents on how to support each aspect of development. (casel.org)
They may not always be able to isolate their fingers to perfectly execute the sign, but if they are able to increase self - expression and communication in support of those very important developmental markers, then they are off to a wonderful start on their expressive journey! (musictherapyconnections.org)