This is going to be long but this is a subject near and dear, and me and my son went through **** the last 2 years so I had to share.
To back up MaryPoppins....don't assume he is not trying.
My son started having problems in 3rd grade, nothing specific, made A's and B's, but had a hard time doing the little bit of homework that was assigned, we thought he was being lazy and just didn't want to try. Also his teacher was terrible and needed to have retired MANY years ago, so we thought that was part of the problem. (She was a problem, but not the whole problem) Then we start 4th grade and because both 4th grade teachers are AWESOME (we go to a small christian school) we said if he has the same problems, then it's more than the teacher. Well, it only got worse. We tried EVERYTHING. Rewards, punishment, helping, not helping, his teacher bent over backwards for us and him trying to figure out what the problem was. We were ALL miserable. Nothing we did helped. Let me add that during all this he was still getting A's and B's. But the effort put into this was unbelievable. Here are some examples:
Homework that should have taken 30 min took 4 hours.
When doing math he wouldn't line the numbers up, so would get the answers wrong
When doing a math paper that was all addition, would start subtracting for no reason
When doing a worksheet in any subject would skip a section even if the section above and below were done.
Could not spell words correctly even when the words were being copied out of a book
Had HORRIBLE handwritting, even if I would make him redo the entire page, he would still be sloppy
Would do homework and forget to turn it in
Would get answers wrong even when paper was done together in the class with the teacher giving the correct answers
Could not follow the directions on an assignment
I could go on and on. We were so frustrated and we truely thought he just wasn't trying. We knew he knew the information but he was making mistakes that just seemed so "What the heck?!?" Then one evening I had a light bulb moment and I thought to myself, "there is no way he is doing this on purpose, nor is he just being lazy".
Anyway, decided to have some test done, thought maybe he had ADD. Went to a phyciatrist(wish there was a spell check

) and long story short, he did not have ADD, he had a reading disability (She suspects dyslexia) me and my husband were shocked and were thinking that's not possible he can read just fine. She went over the testing that she did (called the WISC I think), and it showed that he had a very high IQ and any verbal based testing, he did 98% better than kids his age. But the reading and comprehension part of the testing while still in the normal range was 20 points less than was predicted for his IQ. Anything 15 points or more is considered a disability. More testing is scheduled for Oct.
Anyway, I'm in no way saying that all children that have a hard time "getting it together" have a disability. I just wanted to share our story, and let you know in some cases they truely cannot help it. I have a lot of guilt over all the times we got mad

. Just something to keep in the back of your mind if nothing else works.
Hugs to you and your son, I truely feel you pain and frustration.