We moved to fairfax over the sumer in August, applied immediately, and received acceptance letter around 10 days later, and started at the beginning of the year. Our child was entering 4th grade.
Most of our paperwork was still on the moving truck, so we included very little in our child's packet. We submitted test scores, most recent report card (previous school year only), and the letter from the previous school district indicating acceptance to their GT program. We also completed the parent form required for parent referral. We submitted no additional work samples, no teacher evaluation other than comments on the report card, and permanent records had not yet arrived from the previous school. Process was very easy, perhaps because test scores are very high (99.8, and hitting the ceiling on 1/2 of the test) and child had previously been enrolled in 2 other districts GT programs.
If your child's scores are solidly in the 99% + range I am sure it will be an easy process too.