My friend lives in Pimmit Hills and had a child who was slow to reading who got a lot of extra help there and is now doing great half way through elementary school. I think it is a pretty well regarded school and has a decently active PTA although probably not the most active of all the FCPS schools since it is smaller than some others. I know several moms with preschool kids in Pimmit Hills and they like the neighborhood a lot. It is within easy reach of many things NOVA has to offer and quite walkable. There is a website and a facebook page for the neighborhood where you could get more info and a neighborhood moms group that is a spinoff from that.
http://www.pimmithills.org/