Is it illegal to make an open book exam for everyone except one person?

I am a senior in high school. Today we took our U.S. History Final Exam. The teacher walked in and called all the seniors, except me, out of the classroom and to the library. They all took their exam "open book", basically they were allowed to look through the book for answers. I, however, had to sit in the class and do it without my book. There was no justifiable reason for this. The teacher just does not like me. Was it legal for him to do this? I need to graduate just like everyone else!