I kind of get the ?.
I have two boys. They went to private Montessori in NW and tended to wear much nicer things--very preppy look. Not a problem for us since my sister has 3 older boys and we have boxes upon boxes of hand-me down lacoste, polo, button-downs, dress coats, etc.
We moved - my older one now goes to public school Kinder (going into first grade). The little one is at a very play-based preschool with loads of dirt and outdoor play, etc. I never dress them as nice as I used to. I still don't send older one to elem school is sweats or gym shorts. He wears nicer shorts or jeans, cords, etc. However, I do send him in t-shirts, sweathirt, etc. I save all of the nice hand-me downs for special occassion, class pictures, etc. He is 7 now and is embarrassed to wear a collared shirt to school

--not many of the boys do so I don't push it.
Little one wears really ratty looking clothes (IMO)--sweat shorts, graphic tees, etc. Key is they get filthy, he's happy and they are easy for a 4 year old to pull up and down.
I find knit polos too hot for DC summer/Indian summer so I do nicer tees. I want them to be comfortable.