If the Judge does go against them then maybe the parents should break out into the Father’s Prayer at the Graduation at a pre-set time. Good luck trying to get an injuction against that.
From memory (which isn't always great) the SCOTUS ruled in favor of prayer as long as it was student led some years back. It cannot be compelled by a school but if the students decide to have prayer...
I don't know what happen to that ruling or why it is discounted in these cases.