Criticalthinking company publishes many books to prepare you for Cogat and NNAT test required by GT screening.
http://www.criticalthinking.com/searchBykeyword.do?code=p&catalog=p&searchKey=Cognitive%20Abilities%20Test&directory=test&gclid=CIX47ZKplJoCFQNfFQodwiF1Lg

Back in 2002-03, GTAC members received a document showing 19 students admitted to the GT Center program from the six Cluster IV elementary schools that would feed into Riverside:  Fort Belvoir (3); Mt. Vernon Woods (3); Riverside (3); Washington Mill (6); Woodlawn (2); and Woodley Hills (2).  GTAC members also received information about the number [...]

Advantages of local -
1) Obviously, if your child has good non-GT friends in the local
school it’s easier to maintain those friendships. They will see each
other at recess, on the bus, etc.
2) It’s very likely that a high percentage of the other Level IV GT
kids from your elementary school will stay at the local ES, again,
making [...]