Take your country for example, take all the different levels of government spending on education...and dived it by the number of kids.....that's a lot...on average,it's about 10K dollars per year per student in a developed country...
now consider
how many kids there are in a class ( 25-40)
how much of what they're learning is useless to them or just crap in general
what they could be learning or doing instead of learning useless boring stuff
bullying
and this is not all...not by a long shot..also
most houses are empty during working hours,and may be rented as classes
four students,under current spending standards,could pay one,full time teacher salary per year (40K$) (that means the other 21-36 are paying the OVERHEAD)
One could argue that the school aren't supposed to be good. They are in place as currently designed to mold children into worker bees who do what they are told, follow rules and respect authority.