Set Your Mind
I began studying an appropriately dumbed down version of set theory in elementary school, and my reaction was more or less "Hey, that's obvious. Why I need to study something that's just obvious?". The reason it happened is that set theory deal mainly with logic, and logic is something we have hardwired in us (well, most of us...)
Later on, studying set theory more in depth, I realized it's not so trivial - but it remians quite intuitive. Its biggest utility is that first of all it teaches logic, and logic is fundamental to make cogent arguments and understand them. Second, the idea of sets - their properties and operations - is a great thought-organizing tool.
While the lack of logic and thought organization are severe problems of this age.