Alex expanded on what I was saying perfectly...We've changed enough in this Country to suit certain cultures. I'm Australian with an Italian background, and I'm not a racist, but when little kids these days can't enjoy talking about Santa and the Easter bunny, can't say merry christmas because you might offend someone, you have to say happy holidays... etc because it offends other religions/cultures/nationalities, and those people have their own schools, where they're free to celebrate and worship what and whoever the f**k they want, then they have no right to whinge when something like this happens.
If the fact that you're not allowed to leave school for your religious holiday is that much of an issue for you, go to a muslim school where I'm sure you'd have the day off for it. If you'd rather be at a regular school for whatever reason, then sit there and cop it when you can't have it all your way.