I found this very helpful to parents:
http://www.fcag.org/documents/summerguides/summerguide2009.pdf

Nysmith sends more students to TJ every year. It’s very good. Potomac is also a good school. Some Longfellow students turn down TJ to attend Potomac. Flint Hill is also good.
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Nysmith School
Head of School: Kenneth Nysmith – blog@nysmith.com
Religious affiliation: None
Basic Background: Established in 1983
Accredited by
NIPSA (National Association of Independent Schools)
SACS(Southern Association of Colleges and Schools)
CASI [...]

Top 100 N.Va. Elementary School Scores on Standards of Learning This chart ranks the top Virginia elementary schools in the Washington, D.C., area. Ranked schools had complete data for the number of students rating “advanced” on state tests of reading and math.
Rank Elementary School Advanced in 2003 Advanced in 2008
1. McKinley Elementary 49% 79%
2. [...]

In 2001-02, FCPS required a minimum IAAT percentile score of 98%ile, plus a good score on an exceptionally difficult “Math Seven Assessment” test.  That was the first year of a FCPS 3-year extreme anti-acceleration regime.  In 2004-05, the pendulum started to swing, the required IAAT score dropped to 95%ile and the killer MSA was replaced [...]

Virginia State Science Olympiad  http://www.virginiaso.com/
Here’s an announcement about an April 1st informational meeting on the
new Division A (Elementary School) Science Olympiad program for third
through fifth grade students. 
Dear Parent or Teacher.
 
You are invited to attend the 2009 Division A Science Olympiad
informational and training program on Wednesday, April 1, 2009 at
Sangster ES from 7-9pm.  (Parents with no [...]