I am reading through your post and thinking, geez, this are all the symptoms of ADHD (of course,being the CL here-
http://www.medhelp.org/forums/ADD---ADHD/show/175) I see this all the time.
So I was not surprised when I got down to the end and saw the diagnosis. Nor was I surprised at your problems. I have seen that a lot too. It really is very common (believe it or not). You are dealing with something that you have no experience with. The standard techniques for discipline go out the window when dealing with ADHD.
The key is information. Lots and lots of information. That is one reason why counseling will help. Make sure that at least one of you is involved. You really need the info at this point more then he does.
The first thing is that you must realize that the medication while helpful, is no magic fix. It cannot fix 5 years of not getting the material at school. He is probably very behind in many subjects, and he cannot make that up over night. Also, do you have a 504 plan or an IEP for him? That is crucial.
Wow, there are so many things to say, Its hard to know where to start. Well, stop the spanking, would be the first.
So lets start with what can help at home. This site has a huge amount of resources that you will find helpful. Read as much of them as you can! Everyone can help you. But the link I am sending deals with discipline at home. It will make all of your lives easier. The link is - http://www.additudemag.com/resource-center/adhd-parenting-discipline-behavior.html
Oh, I also should mention that doctors typically start a child off at the lowest dose of medication and wait for parent feedback to know when to increase the dose. Many times, the parents have not been properly informed as what to expect and stop the increase too soon. You didn't say which medication he is on - but this chart lists the length of duration for all the meds. If the medication does not last as long as it should, then an increase might be needed. http://www.leeheymd.com/charts/adhd_1.html
The main thing is that both your husband and you need to be on the same wavelength (well, this is true for any type of child changing behavioral methods). Once both of you understand what is going on with him, you will see a big change in your household. So, actually, unless, he wants to do a lot of reading - both of you should be involved in the counseling.
I hope this helps. Please feel free to ask more questions either here or on the ADHD site which I also monitor. Best wishes.