It was not mentioned today at my granddaughter's school, when I reminded her with this image, she was upset it was not mentioned all day in any of her classes. And if someone brought it up, the subject was changed.
9/11 is a very sensitive topic for any school, which is probably the reason why it’s avoided. But I think you’re right that it’s an important event to remember. Whether it has to be some kind of holiday is another question... may I ask: What is this image? Who made it? What is the meaning of Patriot Day or “9/11” to you?