Force people to pray? How is that even possible? I was a substitute teacher in the public schools. We cannot even get the kids to class on time. They won't even sit down, unless they are in the mood.
The previous poster is correct. Christians (at least in modern times) don't force people to do anything.
Here's what could happen: At the beginning of the school day, someone comes over the PA system, and intones, "Let us pray...," with the clear understanding on everyone's part that there are no consequences to not praying. The atheists have their moment of silence, while the Christians pray.
Would that make the earth stop spinning on its axis?