Kid told he can’t bring Bible to school

So an 8-year-old autistic boy brings his Bible to school to read during his free time.
The school decides one day that he can’t bring it to school anymore. Why? If he is reading it to himself during his free time then what is the problem?
If it was Harry Potter, the koran, or some other book, I bet they wouldn’t have a problem with it.
So why ban the bible from the school? I could see if he was reading it out loud. Then you ask him not to. If he keeps reading it out loud then go from there.
Are people really so afraid of a book?

Precious 8-Year-Old Autistic Boy Brings His Bible to School Every Day – That Is, Until the School Told Him the Book Is ‘Only for Church’