Auditory Processing Disorder (APD) is a condition that is believed to affect 1 in 10 children, but currently the majority of sufferers are undiagnosed and there's still a lot of people who work with children who have either not heard of it or have no experience dealing with it.
Children and adults with APD have perfectly normal hearing but the brain does not process the sounds properly. A book about the condition describes it as "listening through water". For the undiagnosed child, life at school can be pretty tough as all the normal background sounds in the classroom drown out what they need to hear and their academic attainment suffers.
If you have a child who is not doing very well at school but no one can tell you why, then you may need to get them checked for APD.
I have written an article about APD here. I describe the process we went through to get our daughter diagnosed on the NHS and there's links to other websites, where you can get more free info.
Once a child is diagnosed, then for many all you need do is implement simple strategies at home and at school and you should see an improvement.
I hope you find the info helpful.