Deaf schools are pretty much like immersion schools, bilingual schools, etc. The notion of "deaf school" or "school for the deaf" as isolated or segregated is entirely misleading. This notion is influenced by the phonocentric ideaology.
Deaf people are bilingual-bicultural that attending a bilingual ASL-English schools are very important for Deaf children in the same way hearing bilingual Spanish-speaking students are given a positive cultural-lingual identity and efficient access to education in native Spanish and fluent/native English.
The first school for the deaf in the world was founded by Charles-Michel de l'Épée in 1760 in Paris, France. This deaf school, "Institut National de Jeunes Sourds de Paris" (INJS) is bilingual, where French Sign Language (FSL) was used.
Subsequently, more bilingual schools for the deaf were expanded across Europe. Aboard, American School for the Deaf (ASD) was founded in Hartford, Connecticut, in 1817. Eventually, more deaf schools were popped across the U.S. and Canada.
In the 1980s, the idea of mainstream school became prevalent in name of "Least Restrictive Environment" (LRE), which was unfortunately the opposite. As a result, several deaf schools were closed and a number of Deaf students in deaf schools gradually dwindled from 1990s. Many mainstream deaf kids felt isolated and segregated, yet some of them decided to transfer to deaf schools where they find much happiness.
Today in the 21st century, deaf schools are seen as bilingual schools. A bilingual school, "Alberta School for the Deaf" in Canada recently welcomes codas (hearing children of deaf parents) and sodas (siblings of deaf children) to enroll in this bilingual school as a pilot.
You may also be interested in: education of the Deaf.