Which Americans know the most about religion? It turns out to be those annoying atheists:
http://www.pewforum.org/Other-Beliefs-and-Practices/U-S-Religious-Knowledge-Survey.aspx
Atheists and agnostics, Jews and Mormons are among the highest-scoring groups on a new survey of religious knowledge, outperforming evangelical Protestants, mainline Protestants and Catholics on questions about the core teachings, history and leading figures of major world religions.
Unfortunately, they did not specifically track Mennonites. I suspect Mennonites would have done about average, unless the questions veered off into farming lore.
Another interesting finding:
I've long believed that most people who want prayer and religion in school don't really want prayer and religion in school. They want their version of prayer and their version of religion to be dominant over other forms of prayer and other religions in school.
For instance, if we allowed prayers to Jesus in school, we'd have to allow prayers to Allah as well. And if there were prayers to Allah at school, you'd find support for prayer in school drop like a stone tablet.
As such, it doesn't surprise me that so many people don't know about the legality of a comparative religion class or that you read from the Bible as literature. That's not what they are fighting for.