I think the big mistake in schools is trying to teach children anything, and by using fear as the basic motivation. Fear of getting failing grades, fear of not staying with your class, etc. Interest can produce learning on a scale compared to fear as a nuclear explosion to a firecracker.
A plongeur is a slave, and a wasted slave, doing stupid and largely unnecessary work. He is kept at work, ultimately, because of a vague feeling that he would be dangerous if he had leisure. And educated people, who should be on his side, acquiesce in the process, because they know nothing about him and consequently are afraid of him.