Fine, you may want to start with the false belief of /dumb = mute = lack of intelligence/ instead of only 'unable to speak' or that people that do not speak clear and concise English are not as - whatever- ...
How the schools (used to/currently) label anyone with a language delay with processing issues not hearing issues...
How the general consensus of a 'deaf' school is for the kids that can't keep up in regular school, or how 'everyone' should 'want' to hear and not wanting a child to hear and doing everything towards that goal is (whatever/abuse) ...
I still don't see how opinions are going to make a thesis tho-
You might what to find out -why- there are gaps in research, maybe it was done, there was no significant statistical difference between the control group and the deaf group data- and the thing was scrapped as no further data was needed...
