In the United States, K-12 public schools are legally required to educate all children, regardless of immigration status.

many school districts have tried to keep unauthorized immigrants out

But for the last 30 years, many school districts have found ways to prevent unauthorized immigrant students — or the children of unauthorized immigrant parents — from enrolling in their schools. The federal government keeps coming up with new rules to enforce the right to public education, and schools keep finding new ways to evade the rules when it comes to unauthorized immigrants.

So, this week, the US Department of Justice and Department of Education released yet more federal "guidance" for schools — a list of dos and don'ts that spell out how schools should interact with immigrant families. For instance, schools aren't allowed to require parents to provide Social Security numbers or drivers' licenses before enrolling their children.

But this new guidance is hardly the first step that the federal government has taken to try to ensure that all immigrant kids and first-generation Americans can go to school. And it likely won't be the last. While the federal government has declared public education a right, guaranteeing that right has been much more difficult.

US public schools are required to accept immigrants

The right for immigrant children in the US — regardless of status — to enroll in any K-12 public education that was open to US citizen children was established in a 1982 Supreme Court case, Plyler v. Doe.

A 1982 Supreme Court decision established the right to public education, regardless of immigration status

Yet that Supreme Court decision didn't automatically change the policies of individual public schools. And there were still plenty of ways that schools could make unauthorized immigrant families unwelcome, like asking parents to provide their students' Social Security Numbers, or asking students what their visa status was. These rules created what lawyers refer to as a "chilling effect" — they strongly discouraged immigrant families from exercising their rights.

So, in 2011, the Department of Justice and the Department of Education issued a "guidance" letter to state education departments. The letter reminded states of the 30-year-old Plyler decision, and put the burden on school districts to make sure they weren't de facto prohibiting unauthorized immigrants from enrolling.

That guidance might have inspired some schools to become more welcoming. But plenty of school districts took advantage of the fact that the federal guidance only prohibited a few specific policies. Mostly, it limited what information schools could ask from students. But if school districts and states wanted to find new ways to keep unauthorized immigrant families out, they could just ask parents or schools for information, rather than students themselves.

Many school districts still find ways to exclude immigrants

The Department of Justice and Department of Education now say they have received 17 complaints about discriminatory practices since the 2011 letter. Some of these cases explicitly violated the Supreme Court's 1982 decision.

The feds have received 17 complaints of discrimination since 2011

In Michigan, for example, the state legislature appropriated over $1 million in 2014 for schools to help English-language learners — but dictated by law that schools could only apply for funding if they could demonstrate that none of the money would go to help children who were unauthorized immigrants.

The Department of Justice warned Michigan this was illegal. Finally, Michigan agreed to tell schools that the federal government thought the immigration-status requirement was illegal — but the original state law remains on the books.

Other schools rely on intimidation to keep immigrant students out. When Alabama passed an anti-unauthorized-immigrant bill in 2011, one provision required public school teachers to record the immigration status of their students, and submit it to the state once a year for a "report."

hundreds of students stayed home the day alabama's law took effect

The Alabama bill didn't say that anything bad would happen to students who reported that they or their parents were unauthorized. But it didn't have to. Hundreds of students across the state stayed home from school the day the law went into effect, as families were scared that the results of the "report" would be sent to law enforcement or federal immigration agents. The federal government sued to block several provisions of the law, and a judge struck down the school provisions after they'd been in effect for a few weeks.

But the federal government doesn't know what every single school district around the country is doing. These rules only get addressed if individual parents manage to seek legal help. "If the parent gets to an advocate who starts waving around the Supreme Court decision and the (federal) guidance, after a few weeks, the kid gets enrolled," says Karen Tumlin of the National Immigration Law Center.

There were also schools whose policies didn't explicitly go against the federal government's 2011 guidance letter. For example, that letter warned schools that if they were asking students for their Social Security Numbers, they needed good reason. But it hadn't said the same for asking about the Social Security Numbers of students' parents — and sure enough, the federal government has had to challenge several schools in court, including cases in Georgia and Florida, for doing just that.

Fighting policies like this, Tumlin says, is a matter of "arguing by analogy." Advocates had to convince school districts that asking parents for their Social Security Numbers was just as bad as asking students for theirs — even though the federal government hadn't said so explicitly.

The federal government's newest guidance, released this week, adds asking parents for Social Security Numbers (among other examples) to the list of prohibited behaviors. But there's every reason to think schools will continue to come up with new and creative methods to deter unauthorized immigrants from enrolling.

The next battle: parent-teacher conferences

can schools fingerprint parents who come to school plays?

Here's one example: Tumlin says that one "more and more common" school policy is requiring parents to submit their Social Security Numbers — or even their fingerprints — before accessing school grounds for parent-teacher conferences or school plays. The new federal guidance doesn't explicitly ban this. Advocates will have an easier time arguing that the new guidance prohibits this sort of practice "in principle" — but it's just another case of argument by analogy, and schools may not agree.

The new guidance reminds schools to "review the list of documents" they're asking families to provide when students enroll. Essentially, they're asking school districts to make sure they're in compliance with the law, and not asking anything of immigrant families that's tantamount to discriminating against them. But just as previous federal reminders didn't automatically change policies, this one won't either. More likely, when a school district does try to restrict enrollment, immigration advocates will just have an easier time getting it to back down by presenting it with the federal government's explicit do's and don'ts.

Ultimately, Tumlin says, guaranteeing access to public education comes down to this question: "Does each person at every school district in the country understand that their policies have to really ensure equal access?" She thinks both the federal government and local advocates are going to have to keep an eye on school districts under the new guidance, just like they did under the old ones.

No matter how much the federal government does proactively, guaranteeing the right to education is still a matter of waiting for schools to violate it.

Correction: This article originally said that Plyler v. Doe established a "right to an education" for all children regardless of status. It's more accurate to say that Plyler guaranteed equal access for immigrant children to any K-12 public school that provided education to US citizen children. The article has been clarified.