The right not to stand during the Pledge Of Allegiance?

Only if your school is a public school. If it is a private school, they can do whatever they want. If yours is a public school, you are absolutely correct. I did serve 20 years in the AF to protect your right to freedom of speech and religion, and my opinion of your choice is of no concern; it's your right and no one can take it from you, except for the private school system.