Run your church's float in the city's 4th of day parade. No problem.
Authority-endorsed prayer over the public school intercom: big problem.
Praying in tongues in the middle of English class at the public middle school: big problem.
Praying without coercing one's neighbor or disrupting the public educational process: no problem.
NONE of those should be problem if no one is being coerced into taking part.
Why on Earth would anyone have a problem with a school having a prayer over the loudspeaker for those who with to participate, regardless of the religion? Assuming appropriate content I mean.
Are you incapable of just sitting still respectfully for a few moments?