It depends. If you attend a private school, the First Amendment will not protect you from any restrictions your school places on your right to protest. (The First Amendment prevents the government from punishing you for your speech. It doesn’t prevent a private organization for punishing you for your speech.)
If you attend a public school, you do have First Amendment rights, even at school. However, your rights are more limited than the rights of adults. Your school can punish you for taking part in a protest if it causes substantial disruption of school activities, or if it invades the rights of others.
This standard was established by the Supreme Court in a case called Tinker v. Des Moines Independent Community School District. The students in that case wore black armbands to school to protest the Vietnam War, and were suspended for refusing to take them off. The Supreme Court found that their First Amendment rights had been violated, because the armbands were considered a non-disruptive expression of their political point of view.
You may decide that you are willing to incur those penalties, but remember to consider alternative methods of advocacy and protest as well. Sometimes civil disobedience–challenging the rules on matters of conscience and policy–is justifiable. But sometimes there are several different ways to achieve the same goal.
This is may be a fire code violation–contact the proper authorities if you are concerned.
You may not be able to vote–but you have the First Amendment rights to speak, assemble, and petition.
Organizing marches and rallies can raise public awareness for your cause. Doing so off-campus and outside of school hours will be protected by the First Amendment. Reach out and collaborate with as many people as possible–parents, teachers, school administrators, and members of your community–in order to have the greatest possible impact.
The right to petition means the right to ask for the laws that you want and speak out against the ones that you don’t want. Contact your elected officials and tell them what you think. Letters, phone calls, and personal interactions at town hall meetings have more of an impact than emails and tweets. Contact your Senators and members of Congress, since they’re elected to serve you. Don’t forget that state and local officials also make laws that impact you. The My Reps website allows you to find and contact your federal, state, county, and local elected officials. This guide by former Congressional staffer Emily Ellsworth contains some very helpful tips on what you should say and do.