This is a really funny article for me to see, because I am currently sitting in high school, ignoring my teacher who is teaching this book. Great timing.
English is fundamentally a culture class. The goal is to instill certain values through required literature. From what I recall the Great Gatsby is mainly about the ills of great wealth and gilded age capitalism.
If you talk about the themes of the book in a supportive way you're certain to get better grades. Don't just recap what you've read, endorse what they are trying to teach you and you'll be a much more successful English student.
In the US (at least several decades ago when I was in school... I'm old) this was sadly not true for AP English.
It's very much about understanding the themes not just recapping what you read. But there was no propagandization involved. Mein Kampf was a summer reading choice although I think I ended up reading Grapes of Wrath.
Sure, I didn't mean to come at this with a view that it's propaganda. Rather, they're trying to instill values that make you a good citizen. Looking back on my comment it does come off as rather cynical. Probably because I had a rough time in English class and I spent most of my time making summaries rather than making insights.
