Asymmetric Normal Hearing
I am also a parent of a 9 year-old child and can empathize with your frustration when you recognize the existence of a problem that no one is willing to treat. Hearing loss comes in varying levels, yet it is generally agreed upon that hearing levels between 0 dB and 15 dB are within the normal range and do not constitute a hearing loss. It is certainly possible that the levels your child hears are creating some academic difficulties for him although it is also possible that these difficulties are unrelated to hearing. Traditional amplification through the use of hearing aids would be inappropriate for hearing levels that are within the normal range.
However, let me suggest two options which could be beneficial regardless of the actual origins of any academic problems your child is experiencing.
First, I would suggest you ask your child's audiologist if he or she has a compilation of classroom management suggestions for students with hearing loss. While such suggestions are actually written for children with poorer hearing levels than you report for your child, they are suggestions that have been found generally useful with children who have academic difficulties from other sources as well.
Another alternative would be to investigate the use of soundfield amplification for your child's classroom. This involves a wireless microphone that the teacher wears which transmits instruction to strategically placed speakers within the classroom. These systems have been found to improve academic performance for all students in a class and to make the teaching experience more enjoyable for the teacher as well. Again, your audiologist would be a good source of information on these systems.