oralism

The idea that deaf people should be taught how to speak orally from an early age, and that communication through sign language should be actively discouraged. This view is founded on two assumptions, which are now both believed to be false:

• The gestures of deaf people is of the same nature as the gestures of hearing people, ie. extralinguistic or nonlinguistic. They cannot be used to build complex sentences, such as in spoken languages.
• If deaf children are allowed to communicate through gestures, it will displace the ability to learn language, and thus provide them with a severe disadvantage in the communication with hearing people.

The nature of sign languages as complete, complex languages weren't understood until very recently, and thus, oralism has been regrettably common for a long time. I have heard a story about a teacher of deaf children who was reprimanded by the headmaster for speaking with her pupils in sign language. That happened in the 70s. In the decades before that, children might even be punished for using sign language in the school yard or in the dorm room.

Today, even though speech training is still practiced, most schools for the deaf are firmly rooted in the manualist tradition -- which means that they teach deaf children a sign language as early as possible, so that it becomes their first language.