All eyes are focused on the Trump administration’s plans to abolish the Department of Education, provide states with more control over schools, and expand parental choice. Meanwhile, the nation’s most successful school choice strategy will face one of its greatest challenges later this month, when the Supreme Court takes up the case of St. Isidore of Seville Catholic Virtual School v. Drummond.

On its face, the case presents a simple issue: Does a state violate the First Amendment’s Free Exercise clause by excluding a religious school from its charter school program? Religious entities can in fact house a charter school and offer wraparound services to charter students. But, because charter schools are public schools, they are not allowed to offer religious instruction during the school day.

This case is not ultimately about whether public schools can proselytize, however. The outcome will hinge on whether the court deems charter schools to be “state actors” for purposes of applying the federal Constitution. The Establishment Clause requires that district schools, as state actors, be secular. To rule in St. Isidore’s favor, the court would need to redefine charter schools as private schools. Doing so would permanently impact charter school laws in the 46 states that have enacted them.

Today, nearly 8,000 charter schools serve almost 4 million students around the country, with many more students on waitlists. Allowing a religious organization to run these educational institutions may seem innocuous to those who wish to offer a more varied menu of options to families. Yet designating charters as fully private would present an identity crisis for a school sector that has long conceived of itself as—and fought to protect its reputation for being—public.

Identifying charter schools as private could also jeopardize the myriad federal and state funding streams they currently qualify for—funding that the sector has fought hard to secure and continues to fight for on the premise that students attending public charter schools are entitled to the same funds they would receive in district schools.

Charter schools first emerged in 1991 in Minnesota, where educators desired autonomy to teach unencumbered by district rules and regulations that often hinder teachers from innovating in their classrooms. Charters soon caught the attention of both Republicans, who hailed their entrepreneurial spirit, and Democrats, who saw them as a way to expand choice within the public school framework.

The leaders of the charter school movement, for their part, sought to bring public education back to its original mission: to create schools rooted in the communities they serve rather than controlled by distant bureaucrats. Despite opposition from the education establishment, charter schools have grown more popular over the decades because they have delivered results, especially in underserved, low-income communities. During the pandemic, charters attracted nearly 450,000 new families, while district-run schools lost 1.4 million students. In the post-pandemic years, charter enrollment has continued to grow while enrollment at traditional public schools is still declining.

Yet until St. Isidore filed its application to operate in Oklahoma, the notion of a religious charter school was largely theoretical. Yes, some Catholic schools, such as Center City Charter Schools in Washington, D.C., had converted to public charter status as a survival strategy. But these institutions do not challenge the laws mandating that they be public in nature. Schools like Center City must also accept all students who apply (or hold lotteries if oversubscribed) and adhere to the same standards and accountability structures that govern other public schools and those established by their authorizer.

A Supreme Court decision that designates charter schools as private would nullify some federal civil rights requirements (a religious private school can discriminate in hiring against someone who does not share its theology, for instance), but it would not remove the state requirements around admissions practices, standards, and accountability stipulated in their charter contracts. The latter point illustrates the sharp differences between charters and traditional private schools, which have long pushed against adhering to uniform standards and accountability measures.

Since Justice Amy Coney Barrett has recused herself, the case will likely be decided by a narrow margin. With a 4–4 tie, the lower court ruling against St. Isidore would stand.

But a ruling in the school’s favor could paradoxically give charter school opponents a resounding victory. If the energies driving the school choice movement are funneled into private enterprises, public schools could be doomed to remain extensions of the district bureaucracies that have too long controlled them. At a time when the country needs more educational options, not fewer, this would be a major setback for parents and kids.

When the Supreme Court takes up St. Isidore of Seville, it will be deciding much more than one case. The future of public school choice—and the families it serves—is at stake.

Nina Rees is the former president and CEO of the National Alliance for Public Charter Schools.  A longtime advocate for parental choice, she served as the first Deputy Under Secretary for Innovation and Improvement at the US Department of Education.