I don't know your son and where he will be most successful, but my kids have thrived in smaller environments in which they are "normal," and where "services" are just part of the everyday routine, rather than something special for which we have to advocate. (DD is in public now, but a specialized private when she was younger; DS is special/private now.)
Lab is an excellent school. It (and other private schools) will require a recent psychoeducational evaluation, which is a fancy way of saying a WISC plus whatever tests are necessary to diagnose your son's specific learning disabilities and other challenges. If you don't have those tests ready to go, or haven't had them in the past 1-2 years (I can't remember Lab's time requirement) you should start making appointments now, as sometimes it takes a while to get in with the professionals.
Oakwood is the major LD school in NoVA. It and Lab both have a good sense of whom they can and cannot serve; it would be very worthwhile to attend their open houses and perhaps chat with their admissions staff (earlier is better - private school application season will start soon for the 2011-12 year).
Some people on this forum like the McLean School in Potomac as well (to be distinguished from the Potomac School in McLean)

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Newton is a new school that incorporates a lot of physical activity into the day, which can be good for kids with ADHD.