I think undiagnosed hearing loss is alot more common than people realize. I'm a physician and took my son to the doctor constantly, yet his unilateral hearing loss was totally undetected until I asked for an audiology exam.
The whole experience bothered me so much that I have organized for 2 years now free preschool hearing testing in my area. Last year, we tested 160 4 and 5 years old (all had hearing tests at the doctor's, all had health insurance). We found that 10% had previously undiagnosed hearing loss- most of these kids had speech problems.
If you can't hear, it can make you inattentive; ADD/ADHD. I have always wondered how many kids with "ADD/ADHD" really have a subtle hearing loss. HTH.