Everything involved in school shit is costly.
I don't miss those days!
One of the worst things/biggest cons is the uniforms/PE kits. Fucking rip-off. The schools AND the people who produced the uniforms must make a killing from them. They won't let you get a £7 blazer from Tesco, it MUST be the £75 on THEY provide. No reason on earth for this, other than they want to make a fat profit from parents.
Then there's the 'your child has won the chance to have their short story published in a book' con. 200 OTHER children had stories and poems published too - in the same book. And the book was available for sale, for £18, and £15 for additional copies for the nans and grandads, and the aunties and uncles etc.. Fucking con. 
Re: working parents vs non-working parents with kids at school. Me and DH have always worked, and I can tell you that some 'single' (non-working) mums seemed to have a lot more surplus income than WE did.
It helped that they got everything free... rent, council tax, school meals for the kids, free school holidays for the kids, free dental, free prescriptions, and all sorts of concessions. Whilst we had to pay for EVERYTHING. With 2 kids only 14 months apart in age. Not benefit bashing, so don't pull that shit out. I am stating a fact.