Yes, while you are in a public school, you still have your First Amendment right to free speech. However, because it is so important for schools to properly educate the youth of America, a student or teacher may be prevented from saying something if it will disrupt the educational process.  What this means is that it is perfectly okay for a student to say what is on his or her mind, just as long as it does not disturb the class or is obscene.

For example: a student can say that he or she disagrees with the president; but, the student cannot use dirty words to express his or her opinion of the president; and the student cannot say something if it is going to stop the teacher from being able to teach or stop the other students from learning. 

This issue frequently comes up where students are sent home for wearing inappropriate clothing or forced to turn their t-shirts inside out. This issue falls under freedom of speech because even if something isn't spoken, it is still an expression. Usually, school officials do this because what the student is wearing is obscene or offensive. School officials do have the right to do this. However, if a student wore a t-shirt with a political message that was not offensive or obscene, school officials cannot force the student to turn the t-shirt inside out. A good example of a non-offensive, non-obscene political message is a political campaign t-shirt which says something like “Huckabee ‘08” or “Edwards ’08.” In this example, the student is expressing his or her political views, but is not being obscene or offensive. 

However, this only applies to public schools.  So, if you go to a private school, you may not have the same freedom of speech.