When I was a child, I had a note from my parents that
excused me from religious instruction. This was mainly due to my mother's
wishes. She was as staunch an atheist as anyone I have ever met. I believe the
class was somewhere from half an hour to an hour a week, during which time
myself, a Japanese kid and another boy who I now assume was Jewish, would sit
and draw or read.
It wasn't exactly wasted time, as I have fond memories of how
quiet and relaxing it was. A much more effective alternative however would have been to
have the whole class sit through a session on ethics, rationality and morality as
applied to society as a whole, taken by a real teacher.
