The issue of prayers at school graduations and ball games has also been addressed by the supreme court as recently as 2000 in santa fe v. doe. what is the stance of the court in regard to prayers at such events?

Even though attendance is voluntary, the prayer is unconstitutional because the attendees are forced to participate and because it appears to be a state endorsement of religion.
This would be considered as a violation of the freedom of religion in the first amendment of united states constitution since public schools are considered as a government owned institutions.