It is imperative that hearing be checked (as with vision) for any child who is struggling, to rule out any deficit that may go undetected with the school screening programs. I see children who are being assessed for learning difficulties or speech therapy services quite often. Some times hearing is a factor in that child's struggles. Ask your family doctor or pediatrician to order a hearing test and/or vision test to rule out hearing loss or visual difficulties as a factor.
Aside from hearing loss, comprehension and attention/focus in a classroom can be affected by auditory processing disorders. This means that the child hears what is being said but has difficulty making sense of the message in order to respond appropriately. This is far less common than attention and even hearing problems, but it is worth investigating if there are much larger concerns. Having been a mother of two (now grown) children, I recommend asking the teacher if she/he is noticing a pattern and if having a learning assessment would be helpful. I still advocate having hearing and vision checked first.