I've always found the American obsession with class sizes to be bizarre. After all, Japanese/Korean schools run 50 student classes with very few administrative personnel and they do fine.
The union lords get more profit with more teachers, and can funnel more money to the Democratic party.
Good grief to both of these posts....
There are slight culture differences between the US and those countries. This is especially so in how one treats their elders, the higher level of respect given to teachers and there are less broken homes. You have a stable environment/upbringing and you have better behaved students. Now class sizes in Catholic schools were larger and it wasn't an issue. Of course that is largely because if you misbehaved they could just kick you out. Public schools don't really have the option of culling the flock.