I don't have direct experience, since my daughter is in a younger grade, but I've been impressed by Sam, the new 7th/8th math teacher, when I've heard him talk about his approach to teaching.
http://www.friendscommunityschool.org/page/news-detail?pk=860215
My sense is that there aren't a lot of FCS parents on DC Urban Moms, but you may want to ask your question in the Private/Independent Schools forum.