WASHINGTON  — The Supreme Court dealt an unexpected blow Thursday to the conservative drive for religious charter schools.

The justices announced they were split 4-4 in a test case heard last month from Oklahoma, which blocks the new Catholic charter school in the state.

Justice Amy Coney Barrett had announced in advance she would not participate in the decision. A former Notre Dame law professor, she was a close friend of law professor Nicole Garnett, who led the drive for faith-based charter schools.

Chief Justice John G. Roberts sounded uncertain during the oral argument in late April. In the past, he had said states may not discriminate against religious groups, but Oklahoma’s law applied only to public schools, not private ones that were religious.

Defenders of church-state separation had argued that charter schools by law were public, not “sectarian” or religious. They urged the court to uphold the laws as written.

Four other conservative justices had signaled they would vote to allow the religious charter school.

While Thursday’s split decision is a major setback for religious rights advocates, it does not finally settle the issue of religious charter schools. It’s possible, for example, that Justice Barrett may participate in a future case.

This is a breaking news story and will be updated.