Religious schools are considered private and exempt from taxes and get no money from the US Govt. As a kid I attended Catholic schools (K-12). It wasn't to avoid blacks, or Jews for that matter ( yes, I had a classmate in HS who was Jewish), but because the quality of education was far superior to the public schools in my area. It is also easier to teach when the students have the same background (religious) as a starting point.
U.S. warns governments, bankers Iran sanctions still in place (Reuters)
from the article: The new edicts of Antiochus