Choosing between a language immersion base school and a Level IV AAP center is a good problem to have. If your child stays at the base school he would get pullouts. It's a personal choice whether to stay or go. In the case of DS he didn't seem to be making progress in the target language and it was frustrating for all of us. We moved him to the AAP center and I hate to use the word but he really is "thriving". If you look at the FCPS dashboard for your school - http://www.fcps.edu/fts/dashboard/enrollment/esenroll14-15.html you might get a sense of how many kids go to the center but it's not broken out by grade level.

Not sure my kid falls into AAP category, but I think a few of his closest friends in school will be. What do immersion families tend to do with their AAP eligible student? Do the stay at base school? If they stay at base school, do they receive pullout instruction. Our school is two-way immersion and Title I -- not sure if that matters. Just want to mentally prepare for possible exodus and implications that may have.