Yeah I had a 504 plan in high school and my brother is a senior and has one for his GI problems also.
My parents would set up a meeting every semester with our teachers and us to go over the accommodations we wanted.
It is always so much better to tell them to their face w/ your principle or whomever rather than send them a letter.
Some teachers are always going to give you trouble, but it definitely made life a lot easier having that plan!
I am in college and still set up accommodations w/ mine <img src="i/expressions/face-icon-small-smile.gif" border="0">