BS,
There is no double standard. It is a creation of your imagination.
Prisoners and students have the same rights.
If a government prison or any of its employees issues (by issue, I presume it is bought by the government) religious material to prisoners, it is wrong.
If government employees lead prisoners in prayer or other religious observances, it is wrong.
The government would be establishing religion where there may have been none before
If government allows someone else to provide religious material to prisoners or allows prisoners to pray or conduct their own religious services that's fine if they treat all religions alike. They do have the right to regulate it for reasons of safety and not let it interfere with the missioin of the prison.
If a government school, or any of its employees provides religious materal to students, it is wrong. If government employees lead students in prayer or other religious observances, it is wrong.
The government would be establishing religion where there may have been none before.
If the government allows someone else to provide religious material to students or allows students to pray or conduct their own religious services that's fine if they treat all religions alike. They do have the right to regulate it for reasons of safety and not let it interfere with the mission of the school.