A San Francisco high school principal got a personal lesson the constitutional right to free speech recently after suspending three students who posted negative comments about their teachers on a blog.

The principal also banned the students from prom and graduation ceremonies — that is until civil rights lawyers caught wind of it.

The American Civil Liberties Union and Asian Law Caucus quickly dashed off a letter to district officials telling them that students’ blog posts were constitutionally protected free speech.

The students posted irreverent memes and parodies about teachers and school administrators on a blog in March, things like: “Teaches Pink Floyd for 3 Weeks; Makes Final Project Due In 3 Days; Nags Student Govt About Being On Task; Lags On Everything,” according to the ACLU.

The “principal dragged three students she suspected of creating the blog posts into her office and interrogated them at length,” ACLU officials said in a statement, which didn’t identify the school and only referred to the principal as a female.

In its letter to the district, school officials can only punish speech if it creates a “material and substantial” disruption of the school environment, ACLU and Asian Law Caucus attorneys said.

“Speech does not become ‘disruptive just because a teacher doesn’t like it or finds it offensive,'” the ACLU said in a statement this week. “In fact, criticism of authority figures is exactly the type of speech the Constitution was designed to protect.”

With the letter in hand, district officials took immediate action and corrected the problem, erasing the three-day suspensions from student records and said they could go to prom and graduation activities.

“We were delighted by the district’s response,” said ACLU staff attorney Linda Lye. “It was a fantastic teaching moment I think for everyone … The awareness and education level about free speech on the Internet is not what they should be.”

Lye added that the students removed the posts and said they didn’t intend to be disrespectful. But punishing protected speech “is not the way to model respect and authority,” Lye noted.

District officials agreed.

“We absolutely recognize and value our students’ right to free speech,” said district spokeswoman Gentle Blythe. “We also recognize that we need to educate them about responsible speech. As soon as the district was notified of the school administration’s action, we responded. Part of having authority means recognizing that if you make a mistake you need to correct it.”

And yet, district officials refused to identify the school involved in the incident, calling the ACLU letter a confidential student record. (City Insider challenged this decision, given that identifying the school does not interfere with student privacy rights and that the ACLU letter is a public record, albeit with student names redacted.)

Four high schools in San Francisco have female principals including Washington, Wallenberg, San Francisco International and Thurgood Marshall. (We’re guessing readers will out the specific school in the comments anyway.)