Most of the nonreligious independent schools in DC are pretty liberal and very supportive (GDS, Maret, Sidwell -- REALLY supportive). You can look on their websites and get an idea of how outwardly supportive they are certainly.
Public is harder -- but you should be able to see if they have a school paper, clubs, etc.
And try to figure out if you know any parents -- I've had lots of parents contact me with questions about the school my children go to - sometimes neighbors, work colleagues, or just friend of a friend.