Focus on the Family says more than 650,000 students took part in last year's "Bring Your Bible to School Day."
Some are questioning the legality of bringing the Bible to school.
Jeremy Dys, a lawyer for First Liberty Institute, told Fox News, "Students are not only allowed to bring their Bible to school. They're certainly allowed to read it during free time, in between classes, and even reference the Bible within their assignments and class discussions."
First Liberty Institute is a legal organization that was created to protect religious freedom.
The Freedom from Religion Foundation agrees.
"The constitutional boundaries are simple. Students, of course, have the right to bring their Bible to school on this or any other day," Elizabeth Cavel, a lawyer with FFRF, told Fox News.
But there are fine lines students and teachers cannot cross, Cavel said.
"Public school teachers and administrators may not promote or encourage students to participate in religious events on this or any other day,"
Students also cannot "monopolize the classroom time with reading the Bible."
The Alliance Defending Freedom has issued guidance concerning their legal First Amendment rights when it comes to "Bring Your Bible to School Day."
Legal Rights Memo-Bring Your Bible to School Day by National Content Desk on Scribd