As it is the school system serves the primary purpose of reproducing a workforce and reinforcing the values of democracy and markets.
Leftists being the covert defenders of markets and liberal democracy they are, have the tendency to defend the system of schooling from criticism and even downright praise it proclaiming mandatory education to have been a victory for the proletariat. Schools are often viewed in this light as being a service like healthcare welfare, when it really should be recognized as a tool of enforcement like the police and military. If you were to ask several inner city kid from low income households what they think of their school a response of "fuck it" or "meh" would be far more common than one of enthusiasm and praise for the supposed valuable knowledge has been taught in their curriculum. Despite reforms that have been made in many countries schools are still primarily institutions of enforcement rather than, while of course teaching reading, writing and basic mathematics are a social necessity virtually everything else about schools are set up not with the intention of nourishing the intellect of children but rather ensuring that they become good who produce and consume commodities, vote, and only complain in a "reasonable" matter.If a student is too troublesome the school will gladly throw them out, if they are caught with drugs the police will be called and before they're even legally adults will receive a criminal record. This is what schools are, individual teachers or other school staff with genuine intentions do not change this fact.