K.M.
Have a look at www.wrightslaw.com. Go to the left side and scroll down to the 'topics' section. Click on 'retention'. You will find a wealth of information there.
Has he been evaluated for special education services? There is so much evidence out there that supports the fact that retention is just not the way to go... if they didn't get it the first time, they most likely won't get it the second time. Some kids just learn differently and need the methods that are offered through special education services.
Ask his teacher if she can begin the evaluation process for you. Good luck and keep us posted!