I have auditory processing disorder, so can explain a bit of what its like. When someone talks to me, I can hear their voice- but what they are saying just doesn't connect in my head. Its like listening to a radio so low you can hear the sounds but not make out the words. I also have mild hearing loss. I adapted at a young age, learning to read lips. My DD12 has similar issues, as well as ADHD.
When DD12 was young I would instruct her to "show me your eyes" before talking to her. I used that term because its so easy to shout "Look at me!" in frustration, but much harder to shout "show me your eyes". Once she looked at me, I would tell her what I wanted- "Pick up your toys please". I also taught her to say "Yes, Mom" after I tell her to do something. The purpose of the "yes mom" was so I knew she understood what she was supposed to do. It worked wonders! Like most children she also has "selective hearing", lol.
If I were you I'd check on the selective hearing thing. Most children, even the most helpful and obedient, sometimes choose to not listen. My favorite way to test this is first to give the direction- "Please pick up your toys". If I get no response, I then ask "Would you like some ice cream?". If she truly can't hear me then she won't respond to that one either
Once you have ruled out selective hearing, do have him look at you. If he is having auditory problems, he has likely already taught himself to compensate by reading lips. When doing any testing, make sure you mention this to the examiner.
Cheers,
ithinkican
