Why are deaf people an important group to study both as bilinguals and in terms of bilingual education?

Chapters 9 to 16 focus on the many aspects of bilingual and multilingual
education. They commence with a broad discussion of different types of
bilingual education, followed by an examination of the effectiveness of
those types. After a focus on systems of bilingual education, the book
proceeds to examine bilingual classrooms, multiliteracies and biliteracy,
and key bilingual education strategies. The underlying questions are:
Which forms of bilingual education are more successful?
What are the aims and outcomes of different types of bilingual education?
What are the essential features and approaches of a classroom fostering
bilingualism?
What are the key problems and issues of bilingual classrooms?
Why are deaf people an important group to study both as bilinguals and in
terms of bilingual education?