i would look into your schools rules and regulations. back in college Samhain fell on a Friday so i took the day off siting religious reasons, one teacher didn't agree so he gave me a zero for the class, the others were more understanding, but when i challenged him, the teacher pointed out the college didn't [at the time] acknowledge Pagan/Wicca as an official religion. which really upset me because
a. there was a prayer room where i meditated with other pagans.
b. my Muslim classmates took all their holidays off no problem
c. he was Hindu
unfortunatly he basically went 'my class, my rules' and closed the book on it. i didn't want to take it further because i was too busy with other classes, and i was getting a 95% in the class, so the one zero didn't really effect my grade [i think i graduated with a 92% in the end] so the moral of the story is check with the rulebook and tell the teacher in advance why you would be missing class.