Some schools have actually prohibited the use of plastic covers already. These fabric ones make a good alternative. They're reusable so you can even transfer them from book to book and come to school with different designs everyday! Here are some of the new designs.
They're also washable so you can keep them looking like new, unlike plastic covers which you need to replace once they've torn or worn out. Plus they even come with their own built-in bookmarks!
Reusable Fashion Fabric Bookovers
Visit their online store here.