It may be that he all he needs is a little guidance and practice with organizational skills, or it could be more serious.
Many very bright students have stealth learning disabilities (or learning differences, however you want to phrase it) that don't come to light until the child is older. Bright kids are often able to compensate for weaknesses, so they aren't noticed until later in the child's academic career.
Here is my personal experience. I was diagnosed with mild dyslexia in 3rd or 4th grade, but it was decided that I was compensating well and I never received any accommodations. The problem was, I was very advanced in some areas and tasks were too easy to keep my attention, and in other areas, most notably rote memorization, I struggled madly and failed. I was accused of being lazy, stubborn and unmotivated, which was doubly hard to take because I had been trying so hard.
Long story short, I almost flunked out of high school and had been demoted to mostly remedial classes while at the same time I posted a verbal SAT scores in th 99th percentile. What a waste, you know? And the worst of it wasn't the waste of academic talent, it was the emotional pain and low self esteem that resulted from the continual academic failure and lack of understanding I received from both the school administrators and my family. Some very moderate accommodations through the school, or the occasional, "I know you are really trying hard" from a parent would have made a huge difference for me.
Now a have my own children, and although they are still young, they are showing many of the same mental traits I exhibited as a child. Here are some good books I have read so far to get prepared for what I am sure will be an interesting ride:
Dreamers, Discoverers & Dynamos: How to Help the Child Who Is Bright, Bored and Having Problems in School
http://www.amazon.com/Dreamers-Discoverers-Dynamos-Problems-Formerly/dp/0345405730/ref=sr_1_1?ie=UTF8&s=books&qid=1202744437&sr=1-1The Mislabeled Child
http://www.amazon.com/MISLABELED-CHILD-SOLUTIONS-CHILDRENS-CHALLENGES/dp/1401308996/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1202744592&sr=1-1Good luck!