Graduating seniors from East Side High School wait for the procession in Cleveland, Miss., in 2016. (Linda Davidson/The Washington Post)

The Southern Poverty Law Center is using a novel legal argument in an attempt to address what it describes as gross inequities between public schools serving majority-white and majority-black populations in Mississippi.

In a lawsuit filed in federal court Tuesday, the organization alleges that poor academic outcomes for black students in Mississippi are a direct result of the state’s failure to live up to the terms of its readmission to the Union following the Civil War.

The complaint hinges on a 147-year-old law that Congress passed to allow Mississippi to rejoin the Union shortly after the state ratified a new constitution that required, as a prerequisite for an educated public and a functioning democracy, a “uniform system of free public schools” for all citizens, black and white.

“Today, Mississippi schools are anything but uniform,” said Will Bardwell, a lawyer at the Southern Poverty Law Center. “If you’re a kid in Mississippi, your chances of getting a good education depend largely on whether your school is mostly white or mostly black. That is not a uniform system.”

Congress allowed Mississippi’s readmission in 1870 on the condition that its constitution never be amended in such a way that would deprive citizens of their right to an education.

But since 1870, the constitution has been changed at least four times, starting with a major revision in 1890, as Reconstruction gave way to the era of Jim Crow, according to the complaint. By 1890 the constitution called for separate but equal schools and directed far more tax dollars to white schools that were much better off than black schools, according to the complaint.

Each revision since then has watered down the requirement for a uniform system of public schools. Today, the education provision in Mississippi’s constitution gives state lawmakers wide latitude to decide how to run and fund public education, saying that they must provide schools with “such conditions and limitations as the Legislature may prescribe.”

The constitution is now an “empty shell of the guarantee that Congress obligated Mississippi to preserve in 1870” and, as a result, the legislature has been able to consistently underfund schools, the complaint says.

The plaintiffs are asking the court to declare that the state has violated the terms of the 1870 readmission law. The complaint names a litany of state officials as defendants, including Gov. Phil Bryant (R); House Speaker Philip Gunn (R); the state superintendent of education, Carey Wright; and the chair of the state board of education, Rosemary Aultman.

In a statement to The Washington Post, Bryant called the lawsuit “another attempt by the Southern Poverty Law Center to fundraise on the backs of Mississippi taxpayers.”

“While the SPLC clings to its misguided and cynical views, we will continue to shape Mississippi’s system of public education into the best and most innovative in America,” Bryant said.

While the weaker constitutional language has hurt all students — Mississippi is among the nation’s lowest-performing states on many academic measures — black students have borne the brunt, according to the complaint.

The four plaintiffs represented by the SPLC are black parents whose children attend two overwhelmingly black elementary schools in Jackson and Yazoo City, both with ratings of D. The schools have a higher percentage of inexperienced teachers than the average in their districts and lack enough textbooks to go around, and the facilities are in poor condition, according to the complaint. At each school, only about 10 percent of children are proficient in reading.

In contrast, majority-white A-rated schools nearby employ fewer inexperienced teachers than average. They offer plentiful technology and a rich complement of extracurricular activities, and the majority of students are proficient readers.

The schools are emblematic of a broader pattern, according to the complaint, which cites state data showing that in schools where at least 70 percent of students are black, the average rating is a D, compared with a B for schools that are at least 70 percent white.

Only two other Confederate states — Texas and Virginia — were readmitted on the condition of safeguarding their citizens’ rights to an education, according to the SPLC’s Bardwell. He said he found no evidence that anyone had mounted a similar legal challenge in those states.