Level IV referrals are due by February 3, 2011, so the screening pool must be known before that date...so the scores should be back in January.
I have an 8th grader in AAP and a 5th grader in general ed-- there is a tremendous difference in the curriculum, as far as pace, depth, working above grade level. The projects in AAP can be quite time-consuming, so if your child is not into doing research it may be more difficult. Also if your child needs constant reminders to finish homework, AAP will drive you crazy!
You can request evaluation for Level II (one subject) or Level III (2+ subjects) advanced work if you feel your child needs more challenge, but not full AAP (4 core subjects). If you miss the screening pool in 2nd grade you can retest once in FCPS, or do outside testing (like George Mason) until you get the best result you can. Also, anyone can take Honors classes in middle school if your child is ready.
Get to know your school's AAP resource teacher-- he/she will be your best advocate.