are similar in some respects to sign languages, while not having all the characteristics of a full sign language, particularly its grammatical structure. Many of these are either precursors to natural sign languages or are derived from them. Manual codes for spoken languages When Deaf and Hearing people interact, signing systems may be developed that use signs drawn from a natural sign language but used according to the grammar of the spoken language. In particular, when people devise one-for-one sign-for-word correspondences between spoken words (or even morphemes) and signs that represent them, the system that results is a manual code for a spoken language, rather than a natural sign language. Such systems may be invented in an attempt to help teach Deaf children the spoken language, and generally are not used outside an educational context. "Baby sign language" with hearing children Some hearing parents teach signs to young hearing children. Since the muscles in babies' hands grow and develop quicker than their mouths, signs are seen as a beneficial option for better communication. Babies can usually produce signs before they can speak. This reduces the confusion between parents when trying to figure out what their child wants. When the child begins to speak, signing is usually abandoned, so the child does not progress to acquiring the grammar of the sign language. This is in contrast to hearing children who grow up with Deaf parents, who generally acquire the full sign language natively, the same as Deaf children of Deaf parents. Home sign Informal, rudimentary sign systems are sometimes developed within a single family. For instance, when hearing parents with no sign language skills have a deaf child, the child may develop a system of signs naturally, unless repressed by the parents. The term for these mini-languages is home sign (sometimes "kitchen sign"). Home sign arises due to the absence of any other way to communicate. Within the span of a single lifetime and without the support or feedback of a community, the child naturally invents signs to help meet his or her communication needs, and may even develop a few grammatical rules for combining short sequences of signs. Still, this kind of system is inadequate for the intellectual development of a child and it comes nowhere near meeting the standards linguists use to describe a complete language. No type of home sign is recognized as a full language. Primate use