You will find other information about the school as well at this website.
The Watertown H.S "Student Handbook" is posted on the schools website and clearly outlines the "Dress Code"
"Student attire should not disrupt the educational environment and/or distract
other students. Students will dress appropriately."
It further describes the acceptable length of skirts, shorts, and shirts and provides guidelines for writing and slogans on clothing.
It's a very standard and "common sense" type of policy.