"Separation of Church and state" was meant to keep one form of Christianity from dominating all the others, not an attack on Christianity.
^^^^^ CB: In Europe, the Protestant Reformation represents/reflects the bourgeois rising against the feudal order, of which the Catholic church is a ruling class institution , i.e. an established church.
In America, which never had feudalism with a Catholic Church section of the ruling class, the Protestant Reformation is victorious and moot ,reflecting that there is no class struggle between lords/bishops and bourgeoisie.
In America, where there is no bourgeois/feudal conflict, the law of separation of church and state (First Amendment to the Constitution) echoes explicitly the European bourgeoisie breaking up the feudal ruling class configuration of church-state.
To paraphrase Chris, separation of church and state is meant to prevent reestablishing a feudal-like Catholic Church in the new bourgeois Christian or Protestant milieu. But it is not an attack on religion, because , well, religion is still the opium of the masses, a tool of class domination.
Maybe
Anyway, the best way to get at this is probably not by reading Calvin or Jefferson, though it might be in their writing in coded or inverted form.
Of course, about the last thing the Texas school board wants is for students to learn a historical materialist version of "World"/Euro-American history.