Well, I taught a child whose teaching assistant (lovely lady and far from well-paid) bought him some trainers when his toes were poking through the ones he had (his only pair of shoes). He was so proud of them and showed them to me. Next day, he was back in his threadbare, outgrown ones. His dad had taken the new pair to the pub and flogged them. I do not joke or exaggerate, THIS HAPPENED.
I know some people hit genuinely hard times - good grief, my own daughter is suffering hugely at the moment - but some parents are feckless. How to tell the difference is the problem.
Re: School uniform, most are supermarket cheap and I never worked in a school which didn't have a stock of second-hand clothes.