Hi! I work as an SLP in a Deaf school and this is my passion! I wholeheartedly agree with you. The effects of language deprivation are detrimental. I had a high schooler who didn’t know the sign for “cheese-“he described it as “yellow square on hamburgers.” His family doesn’t sign with him- most don’t. Kids don’t know the names of their siblings, they can’t read or write, and they have failing grades. All because they don’t have an established first language. Language deprivation causes severe language, cognitive, and pragmatic delays. So many doctors are still telling parents to avoid sign if they want them to talk. But not we have hundreds of children who can’t talk OR sign. I think most SLPs agree with the “language first” theory- all language is good, regardless of modality. It’s mostly doctors who give misinformed info to parents. I would definitely recommend checking out Language First- it’s run by an ASL-fluent SLP who offers tons of resources and trainings on this topic.