The best teacher that train someone to be a plumber is a good experienced tradesman. I know plumbers that have never been to college, but are fantastic at what they do.
Just a thought, if the thousands of young trainees who sat a plumbing course did get a job, where would that leave us? Plumbers already face an ever shrinking customer demand for their services. So existing plumbers struggling to make ends meet would probably become redundant in an over saturated market and the youngsters would quickly follow.
In my opinion.