In short, this is a First Amendment case about the Second Amendment. The groups that filed the suit hope to push back against the many public school districts that lack an appreciation for both free speech and gun rights.
In this case, the Washoe County School District does seem willing to recognize free speech—when it's anti-gun. Two months ago, as proposed anti-gun walkouts were being planned, the school district released a statement saying that "as a district, we have always placed a high value on student voice." And the district (after some initial back-and-forth) decided not to suspend a student who, during an anti-gun walkout on a school day, called the office of Rep. Mark Amodei (R–Nev.) to say, "Congress people who are not acting on gun control reforms need to get off their fucking asses and do something."
Brooke May, a teacher at the school, claimed last month that the shirt violated the dress code and said the 8th-grader could have his "Second Amendment rights when [he] turns[s] eighteen," according to the complaint. The dress code prohibits "obscene" language, anything that "may be deemed a safety issue," and "anything that promotes weapons."
Click on this image to read the full article by DECLAN MCCULLAGH on 4.24.2018 on Reason.com