Suppose you help run a school as a teacher, principal, member of the Board, or as a government council member which oversees the district, and you have a problem with gangs.
In California we have prison gangs which have local offshoots in cities outside the prison such as the Surenos, Nortenos, Nuestra Familia, Mexican Mafia, Mara Salvatrucha and others for blacks and whites. Among the Latino gangs the colors red and blue have been adopted by convention to denote one or the other. There have been innumerable killings simply for wearing the wrong color in the wrong place. Typically, a challenge is called out, "Which group do you claim?" If you claim the wrong group, you can die on the spot. "I'm a natural person," is one way of claiming that you are neither.
Violent gangs also wear gang signs and signals, in addition to colors. They 'tag' walls and buses. Members also wear tattoos signifying affiliation, and flash gang finger signs.
As a public school administrator, you, naturally, want to do something to prevent gang violence and promote safety for innocent students.
The word 'public' is significant here, because public schools are publicly run, meaning governed by rules laid down by government officials, as opposed to private schools. Although for K-12, state law requires the attendance of all school age students at some school, private schools are privately funded and privately administered.
As a public school administrator, you might decide to promote a dress code that would prohibit gang members from wearing their colors and symbols.
But the Constitution guarantees the right of free expression, which seems to conflict with the school policy restricting expression to that which is approved by the school, meaning the government.
Constitutional law recognizes a huge distinction between what you can do as a private person for private reasons, and what you can do as a public official for public purposes. The Constitution speaks in terms of "Congress shall not..." (5th Amendment) and "No state shall..." (14th Amendment). It does not speak in terms of "Thou shalt not..." the way the Ten Commandments does. The one possible exception in the Constitution is the 13th Amendment (forbidding slavery after the Civil War) as that applies directly to private slave controllers.
The cases first recognizing this public-private dichotomy are called the Civil Rights Cases (1883), which seems something of a misnomer, as they have been used to promote the right which you enjoy to practice racial, ethnic, and religious discrimination in private, such as in your choice of spouse and fishing companions. That is your civil right, to discriminate on those bases. It's just that government may not so discriminate, not since Brown v. Board (1954), that is, as modified by Parents v. Seattle School District No. 1, last week, which has attempted to make the Constitution color-blind. The first Justice Harlan, in his notable dissent in 1896 to Plessy v. Ferguson (which upheld 'separate but equal,' thus legalizing Jim Crow) declared that the Constitution was, meaning ought to be, "colorblind" when it came to government law and policy. The problem is that while the document may be supposed to be colorblind, the people who live under it, and administer its interpretations, are anything but. Racial politics is as alive and well as it's ever been, although perhaps more subtle and, sometimes, sub rosa, hence the need for strict scrutiny of legislation impacting one race over another on its face or in application.
Suppose as school administrator you consider imposing a rule prohibiting the wearing of any clothing or accessory bearing labels or logos, or colors, or symbols. That would certainly cover the gang symbol problem, wouldn't it?
Your problem is that you will have great difficulty describing, meaning defining in words, what you want to ban without banning something else that would be protected. This is the problem Shylock had in 'Merchant of Venice,' where his bond allowed him a pound of flesh in case of the default which in fact occurred. The lawyer (female) Portia, argued, successfully, that Shylock could in fact take his pound of flesh, but not one gram more. Shylock, in winning, lost. Why? Because there was no way he could be sure, in advance, that he would not take more than his pound of flesh. No, I don't recall whether he would've settled for less.
Defining prohibited expression is the Shylock problem. If you try to take more, we say, as a matter of Constitutional Law, that you have failed to 'narrowly tailor' your definition to properly fit your problem and are thus prohibiting protected speech that, in this case, a student has as a matter of constitutional right.
BAD TAILORING FATAL
That's the rule. Bad tailoring is fatal to well-intentioned rule-making, which is why in First Amendment law the people who go to bat to uphold the Constitution so often find themselves defending Nazis marching in Skokie, students who are wising-off, or critics of presidents who wish to conquer the world, or at least the parts of the world that we consider vital to our flee-floating interests.
In the article below is an example of a school dress code thrown out by a local judge in Napa who has read his Constitutional Law.