the stuff you learn in school such as algebra, calculus, trigonometry, geometry, history, geography, science, social sciences....etcetera
all these stuff may seem useless like the stuff that you actually learn may seem really useless and you might never actually come across it in life again but these activities or syllabusses or curriculums were developed for our minds to think.
Stuff like geometry... we might never use it again but the crazy questions that we might do... like proving that the angle from a tangent to a chord is equal to angle in alternate segment... that kind of stuff actually gets our minds working. And alot of these questions need a bit of imagination/inspiration to work out.
I live in Australia so the education system is alot different to the American so when we choose maths... we have a choice of picking general, 2 unit, extension one or extension 2; extension 2 being the hardest. Many of the stuff learnt in these different levels (apart from general maths cause thats just the basics needed to survive) isnt really needed but what it does is to get us to think and to excercise our minds. They also give us an indication of our own level, and the feeling of self accomplishment when we've finally solved some crazy ass equation.
So saying stuff like "algebra is useless" is absolute rubbish cos it might not be needed but the way that it trains our brains to think and process information is very valuable and will most likely help us in the real world. So if algebra is considered useless, then maybe doing jigsaw puzzles in preschool schould be considered useless as well cos we will never play around with jigsaw puzzles in our life again but what the jigsaw puzzle does is trains our brains to think and put things together same as what geometry basically is but not as practical.
But then really depends on the person as well, like if they dont want to learn then there isnt really any point in forcing them, but then it usually comes down to the educator as well, if they're actually allowing the student to learn in the best possible way.
So alot of the stuff thats done in school isnt really useless cos its basically a crucial stepping stone to the adult world.