I came here to look around and lo' and behold I found EXACTLY the issue I deal with everyday. My daughter is 10 and is ADD also. She takes 20 mg of Ritalin 3x a day. She sounds like your son Christina. Having a problem with the simplist tasks such as you say.. brushing her teeth, brushing her hair, getting organized in general. Fortunatly she comes home from school and gets a bite to eat (taking a break from school work)and gets right to her homework. This I am so thankful for since she has Basketball, Girl Scouts and whatever else comes up during the week to add to her schedule. I have resorted to buying her a corkboard with 1/2 cork and 1/2 dry erase. I use the dry erase side to put the things she has to do today on it and she checks them off as they are done. The cork board side she uses for things like notes, that help her to remember what is due at school etc.
This seems to help with the tasks at hand, but I still have a battle with the simple things we all do daily, teeth, hair, etc. It is an uphill battle and I know how you feel. I am going to check out Michele's advice about Asperger's Syndrome.
Good Luck! And take care!

I have a 20 yo stepson who sounds like this.  He has been tentatively diagnosed with Asperger's Syndrome.  You might want to do a websearch of this as well as NonVerbal Learning Disabilities if medicating with ritalin doesn't work.

Dear Christina,

As we often hear, "You can talk until you're blue in the face....." Your son is not accomplishing some tasks that you want him to accomplish. Now, how can you assist him in doing what you want him to do? Let's face it, it isn't high on the list of priorities for many (proabaly most) 12-year-olds to brush their teeth and put their clothes in the laundry. But that's not to say he can't be doing a better job. There's no doubt that his ADHD likely makes accomplishing some of these tasks more of a challenge, but it's also true he can do better.

They key is to make it in his vested interest to accomplish the things you want him to accomplish. In order to do this, establish some 'quid pro quos' with him - i.e., things he desires (TV, play with friends, video games, specific bedtime, allowance money, etc.) become contingent on fulfilling his 'responsibilities' (which really means the things you want him to do).

To help him be more orgainized and focused, make lists - morning tasks, after school tasks, evening/bedtime tasks) - and post these in suitable locations where he can easily view them and, literally, check off the items.

You might also want to consider a late-in-the-afternoon dose of regular Ritalin (or a noontime dose of Ritalin SR), since he's really not getting the benefit of medication during his hours at home. This might help with accomplishment of homework (and other tasks).

Finally, does he display any learning disabilities? He's spending an inordinately long time on his homework. There may be some learning disorder which is exacerbating his other difficulties.