I started working at California School for the Deaf back in the 1960s. Most of the kids didn't know American Sign Language (ASL) when they first came to CSD. In fact they didn't know any language at all unless they had deaf parents and were consequently several years behind in learning other things. Since human minds are programmed to learn language in infancy and early childhood, it's much harder for children to learn any language by the time they start elementary school.
I was one of the first two counselors allowed to work with younger students in the lower school who knew ASL. Before that the teachers had punished the little kids, even those from deaf families, for signing because they thought if the kids couldn't sign they would try harder to learn to talk and lipread. Teachers would peek through the classroom blinds in the afternoon and watch the staff on the playground. If they saw counselors signing to the little kids they would get them in trouble. Those teachers were furious when the school hired me and the other counselor who could sign and let us teach the kids to use Sign Language.
Students with any hearing at all were required to wear hearing aids, even though those were pretty much useless for most of them. If the children had any residual hearing it was seldom in the speech range, so amplifying the sounds they could hear didn't help with communication.
The hearing aids consisted of heavy devices much larger than a modern cellphone which were worn in a harness on the chest and connected to ear molds by wires. Even hard-of-hearing kids hated those hearing aids and the students often tried to hide or break them.
The California School for the Deaf was similar to all the other residential schools for deaf or hearing impaired children in the USA at that time, and almost all deaf children were educated in similar institutions.
Of course people have learned a lot in the last 40 years, and I'm happy to say the education of deaf children has improved a lot since then.