It wasn’t really taught in my school aside from one dickhead substitute teacher, but a lot of my classmates were Christian and it was more or less universally accepted among them that YEC was the only valid way to interpret the Bible (including the class valedictorian) and your choices were

1. The Earth was created 6000 years ago in 6 days. This is what the Bible means and this is what everyone always believed it meant until very recently, aside from a few modern liberal heretics. All those scientists across multiple disciplines are either stupid or lying and if you believe them, God will torture you for all eternity after you die.
2. This “Christianity” thing is just a bunch of bullshit made up by people and never would have happened if those Bronze Age shepherds had just had radiometric dating and space telescopes. If Christians are starting to get more open to scientific concepts like an old Earth now, it’s solely because they realize that their millennia-old positions are finally becoming untenable. And if the Christians are that full of shit, why shouldn’t I assume all the other religions are too? Atheism is the way.

As an early teen, I chose 2. In hindsight, it was a very Reddit-esque oversimplification, but I was also a child with minimal knowledge of any religion except Biblical literalist evangelism. I have a much more nuanced understanding of religion now than I did as a kid (I understand that YEC is a relatively recent invention and interpret religion in general through the lens of Marxist–Leninist atheism), but to this day I can’t seriously entertain the prospect of being anything other than an atheist, and I think my childhood experiences are largely responsible for that.