The seperation of church and state
is implied in the 1st amendment
with "Congress shall make no law respecting the establishment of religion, or prohibiting the free
exercise therof." This means that the state
cannot force children to go to a public school
or have a state based
church. This is to protect everyone's religious views to the extent
it does not harm another.
Buses can take kids to parochial and public schools
becuase it is in the best interest of the children
to have that transportation, but it cannot require
a reciting of a prayer.