There are many different trucking schools with all kinds of differences. Everything from the length of the school, to the cost of tuition, to the skills that are taught. The only thing they have in common is the desire to make money off of the guys going through the school.

These schools are in business to make money and turn out licensed CDL holders as quickly as possible. They know that the company that agrees to hire these newbies will spend several more weeks "training" these guys.
Once they get their money out of the newbie they do not want them around anymore.

Its up to the newbie to make the leap of faith (from what he knows to what he hopes will be a bright secure future) and make the transition to a full fledged trucker (which may take several years). A CDL is nothing more than a license to learn while you earn if you really think about it. Kinda like the old time apprenticeship programs.