As a teacher in the district, I am in no way saying that your kids can ride their bikes to school... BUT,  if you want them to ride their bike to school, let them.  No one is going to check, or ask your child when they arrive in the classroom how they arrived to school.  I knew a lot of kids that rode to school last year that lived pretty far away, it was just up to the parents to make that decision.  I believe the "one mile mark" is used so that kids will be guaranteed a bus ride and not be FORCED to walk, ride their bike or find their own way to school.