Separation of church and state is not technically a law. However, SCOTUS ruled against exactly this in Stone v. Graham. My fear is that states are doing this to bait it back to our newly conservative SCOTUS.
More than 40 years ago, in Stone v. Graham, the Supreme Court overturned a similar state statute, holding that the First Amendment bars public schools from posting the Ten Commandments in classrooms. No other state requires the Ten Commandments to be displayed in public schools.