The Scout Association
The Scout Association is an umbrella for various youth groups focusing on outdoor activities. While originally closed to atheists, the UK Scout Association has taken steps to accommodate atheists and humanists.  The Boy Scouts of America is still closed to atheists. 
- "The Boy Scouts of America maintains that no member can grow into the best kind of citizen without recognizing an obligation to God [...] Only persons willing to subscribe to this Declaration of Religious Principle and to the Bylaws of the Boy Scouts of America shall be entitled to certificates of membership."