Working class kids also benefit more from studying than high-SES kids, so as life advice this is kind of dubious. If working class kids don't study then they're still not going to get into college based on their grades/SATs/writing, whereas for wealthy kids they're already going to be fine even if they don't do a ton of work.

Also, given that the school system in part exists to screen out working class kids from elite jobs, if these kids actually started getting great grades and captaining the crew team or whatever then colleges and companies would just start selecting for other things.