do find out the name of the other med. If its Prozac or Paxil, that is not good because it can block the pathways for the Ritalin and allow it to back up and cause all kinds of problems. And, ya, you should always know the names of meds so you can look them up for side effects.
Another thought on meds is that docs always start out low and go slow waiting for parental feedback. Ritalin is good for 4 hours max. the SR version is good for 5 to 8 hours. Ritalin is a good med, but the Adderall type meds can be more effective for some people and can last much longer. Point being, his meds could be running out before he gets home. That can be changed. In fact, from what you have said, it doesn't sound like they are working at school very well either. Have you talked with his doc about his problems at school and asked about a medication increase?
Full chart on meds here - http://www.leeheymd.com/charts/adhd_1.html
Another thought is that it sounds like he has a pretty high metabolism rate if he is always hungry. If that is true, the normal dose of meds will burn through him much sooner then for a normal kid with regular rates.
He should have a 504 or an IEP at school. If he doesn't, they are not helping him as much as they could be.
I would expect him to do poorly in school. You can not make up for several years of lost time overnight.
Having no remorse for the things he has done is not unusual for ADHD kids or bipolar for that matter. But, it does help to know what he has. Did you look at the link I sent you. It gives very specific guidelines for each one. You have to know what he has got for correct treatment.
Since he is taking Ritalin - I would assume somebody thinks he has ADHD (you don't take Ritalin if you are bipolar - well, unless you have both maybe). Has anybody mentioned the ADHD thing to you. Because there is a lot of resources for parents to help them deal with ADHD kids.
A good example is this link
and this site has tons of useful information to make all of your lives easier. I am also the CL on the ADHD site here - http://www.medhelp.org/forums/ADD---ADHD/show/175
and I use the site I just mentioned alot for very specific aids for parents and kids.
Finally, if he is 8 and the size of a 3 year old. That has got to be a very difficult thing to deal with. He has got to come home from school every day feeling very defeated. And if he is doing badly at school, that makes it even worse. He really probably needs psychological counseling to help him through all of this. Is he getting any?