Unless Epping High School has a dress code that bans the wearing of T-shirts by students, its principal was way off base in ordering a freshman to cover up her Trump tee this week.

Case law on the issue of protected speech in schools in this regard is well established. A landmark 1969 case (Tinker v. Des Moines) upheld the rights of students to wear black armbands to protest the Vietnam War. Supreme Court Justice Abe Fortas famously wrote that students do not “shed their constitutional rights to freedom of speech or expression at the schoolhouse gate.”

Well, we thought it was famous but Epping High’s principal, Brian Ernest, likely was not on the planet back then. He may have been earnestly trying to keep things calm when he told Ciretta MacKenzie on Monday to change her “Make America Great Again” Trump shirt.

Since Epping High was celebrating “America Day” and students were urged to show their red, white, and blue, Ciretta thought hers a good choice.

She says Ernest told her he didn’t want anyone to feel uncomfortable about her T-shirt. He also emailed her father, saying, “I explained that we need to separate political views from patriotism. In today’s climate it is important to not mix church or state.”

Say what?

School Superintendent Valerie McKenney, exercising her own First Amendment rights, declined to say anything when our correspondent asked for comment. This is why school supers get the big bucks.

But School Board Chairman Dave Mylott said that he is concerned about this being viewed as a violation of the student’s rights. Mylott plans to address it at the board’s April 18 meeting.

Good for him. And good for Ciretta.

Such incidents are sometimes called “teachable moments” by professional educators. In this case, it may be a student who teaches the educators.