You asked so here you go with some information backed by links that may be helpful to you. The first link is to a set of actual exercises designed to do with young children to try to prevent or improve Central Auditory Processing Disorder (CAPD) problems.
The thing that needs to be understood about Central Auditory Processing Disorder (CAPD) is that it is a biological and/or physiological problem in processing sound. It involves malfunctions in the way the brain handles and interprets sound.
So, for Central Auditory Processing Disorder (CAPD) to be diagnosed with any certainty (as opposed to a language processing disorder) it MUST be diagnosed by an audiologist trained in the techniques required, using a sound booth and specific, well defined methods and tests that can help pinpoint where the problem is occurring. The tests require use of pre-recorded and computer-administered sound patterns so that very tiny differences in the processing of sound can be detected and isolated from other potential causes like language processing defects.
It cannot be done by the school audiologist administering a questionnaire. It cannot be done by a speech pathologist. It might be able to be confirmed or suggested by neuro psychiatric assessment but the actual diagnosis and testing requires the audiological examination.
Many audiologists do NOT have the training, equipment or skill needed to administer Central Auditory Processing Disorder (CAPD) testing so you need to specifically ask about this when you get a referral. often the testing is done at university speech and language centers because true Central Auditory Processing Disorder (CAPD) testing is not a simple process. Usually it will not be covered by health insurance and you will have to pay out of pocket.
You should expect to get a written 2 or 3 page report that specifies the tests administered, the results and the conclusions of the examining audiologist. If the audiologist feels that any problems may be a sign of brain/nervous system immaturity they will say so and suggest re-testing in a set period of time. Central Auditory Processing Disorder (CAPD) testing cannot be done unless the child has normal hearing and a regular audiology screening is included in the exam to insure there is no significant transient hearing loss from things like colds that would interfere with the testing and accuracy of the results.
The age of the child matters due to the maturation of the nervous system. It simply cannot be done in a child younger than 3 or 4. It can be done with caution in a child 7 or younger. After 7 it will be up to the audiologist to determine if there is sufficient nervous system maturation to allow an accurate test to be performed.
Central Auditory Processing Disorder (CAPD) often does affect reading, writing and spelling because the child cannot process the phonemes the way they need in order to be able to decode and encode words (being able to recognize and manipulate the separate syllables and/or sounds). This ability underlies our ability to spell, read and write. Phonological awareness is a key component of reading along with phonological memory. Specific speech interventions can be helpful depending on the specific problems your child has if the speech therapist has the training to do them and knows to do them.
Here's a link to a workbook that can be used to help improve your child's ability and flexibility in processing phonemes. Phonemes are the individual units of sound that make up speech. It is designed with the young child in mind.
http://talkingwithjilld.com/Publications/AUD PROC PHO AWA LIST EXE.pdf
Next is a very thorough and comprehensive document aimed at school audiologists that describes Central Auditory Processing Disorder (CAPD), discusses factors to be considered when referring or considering assessment, the assessment techniques to be used and classroom interventions including the use of personal FM systems when appropriate.
http://www.aitinstitute.org/CAPD_technical_assistance_paper.pdf
Next is an older but helpful and somewhat technical article that discusses possible sub-classifications of Central Auditory Processing Disorder (CAPD) that you may find useful.
http://www.apdukclub.apduk.org/HTMLobj-292/subprofiles_Teri_James_Bellis.pdf
Finally, here is a highly technical article that addresses the need for modality-specific assessment. This is code for using audiological testing and not just relying on other indirect forms of assessment for Central Auditory Processing Disorder (CAPD).
http://aja.asha.org/cgi/reprint/14/2/112.pdf