Given that most definitions of consciousness I've seen essentially express that you are capable of symbolic/abstract thinking, I'd say:

1) (extreme) autistic person that doesn't speak, but can, and arguably thinks too abstract, rather than not enough : yes, conscious. Probably more conscious in some sense than "normal" people, whose consciousness is more a group thing, or at least less independent.

(also: not speaking is a pretty extreme form of autism, certainly not something you'd see in your average school)

2) person that grew up without ever having any reason to learn symbolic or abstract thinking ? No, not conscious

But it's going to be a sliding scale thing. By some measures a cat and a dog are conscious because, well, because they are certainly capable of making humans think they are suffering (and therefore they both think and feel, which is where consciousness definitions are going on now. Fish, for instance, are not). This seems to me a really bad way to define it but it's certainly widely used.