American Sign Language
According to Hrastinski &amp; Wilbur (2016), American Sign Language proficiency is the single most contributing factor to the academic achievement of Deaf students who attend schools that teach with American Sign Language, particularly in the areas of reading literacy and math. Deaf and hard of hearing children who have higher levels of American Sign Language proficiency and those who have higher proficiency in a second language (e.g., English) are those who were exposed to American Sign Language during the critical period of language.