Yes! You've got it right! In schools for deaf children, they were not allowed to use sign language! And in some schools, this is still the case today! Why? Let's hear a brief explanation from Nikola Śliwa in Polish Sign Language (PJM).
In 1880, the International Congress of Deaf Teachers took place in Milan, during which a resolution was passed banning the use of sign languages in schools for the deaf. It was not until 1980, in Hamburg, that the International Congress on Deaf Education was convened, and the ban established a hundred years earlier was lifted. The period from 1880 to 1980 was referred to as “the century of shame.”
Today, it is known that learning sign language does not interfere with the learning of spoken language in any way. On the contrary, proficiency in sign language by deaf or hard of hearing children actually facilitates the learning of spoken language.