Hi, I am also the CL here - http://www.medhelp.org/forums/ADD---ADHD/show/175 and
you may want to continue your discussion over there.
There is a lot that can be done for ADHD kids, both in terms of studying and how they are disciplined. As you are finding out, normal punishments do not work.
But, you do need to know if he does have ADHD - although his symptoms would certainly suggest it. And having two siblings with it would certainly enhance the odds of him having it. Perhaps what ever doctor is helping you with them could also give guidance.
Anyway, here is a good general overall look at adhd.
You might want to get the book, "The ADD/ ADHD Answer book," by Susan Ashley. about $11 on Amazon. You will find it very helpful.
I also have some very specific links on most problems. For example, whether he has ADHD or not this will help with home studies.
Hope this helps. Let me know if you need more info.
By the way, if the school could not handle his medical condition - they should be helping out with his home schooling. You need to talk with the districts special ed department. It sounds like they basically kicked him out due to a medical condition which is illegal.