Hi-check out the FCPS AAP website for all of the info you seek.
In a nutshell, your child will take the NNAT in 1st grade and CoGAT in 2nd grade. Based on these scores, plus teacher recommendations and work samples will determine ulkmate entry into AAP for 3rd grade. Once in, your kid is in through 8th grade. AAP status does not influence course choices in high school.