Yes, private schoold does make a difference. I can guarantee you my public school classmates couldn't have passed that. I was a senior year exchange student in US from souther europe. I'd have no problems passing this end of my sophomore year, actually - but senior year high school in rural midwest - I can guarantee you noone would get 50%.
Actually, most of our students skip these courses if possible. This is required to attend collage in India whether seeking a BA or BS. I doubt few with a BA and many with a BS from collage in the US could pass this test. At least 90% of Congress would fail this test. They don't know a port from a port-a-john.