People cited violation of the First Amendment when a New Jersey schoolteacher asserted that evolution and the Big Bang are not scientific and that Noah's ark carried dinosaurs. This case is not about the need to separate church and state; it's about the need to separate ignorant, scientifically illiterate people from the ranks of teachers.
In a basic agricultural society, it's easy enough to swap five chickens for a new dress or to pay a schoolteacher with a goat and three sacks of rice . Barter works less well in a more advanced economy. The logistical challenges of using chickens to buy books on Amazon.com would be formidable.