The big story here isn't that a state planned to allow public funding of religious schools. This happens all the time through voucher schemes, even though it's unconstitutional. The real story is that the U.S. Supreme Court split 4-4 on this case when it shouldn't have even been close.
Not long ago, Oklahoma planned to allow a religious charter school run by the state's Catholic dioceses. The constitutional problem with this was obvious: The school would have received public funding to sponsor religion. But even Oklahoma's Republican Attorney General didn't support this affront to separation of church and state, and the Oklahoma Supreme Court ruled 6-2 against the dioceses.
Now the U.S. Supreme Court - with only 8 of its Justices on the case - has split 4-4 on the matter. This means that the lower court ruling stands, and that you can't have religious charter schools. The real shocker is that it was 4-4 instead of 8-0. Because of this deadlock, similar cases could be tried later.
In brief, religious charter schools are unlawful, as they constitute taxpayer sponsorship of religion. This is basic constitutional law. There is no wiggle room on this. Sometimes you can see how courts can disagree on how to interpret constitutional law - after all, that's a main reason we have courts - but this is a case where there is absolutely no ambiguity. Yet the Supreme Court has drifted so far from even the most basic legal principles that they ruled 4-4 instead of 8-0.