The number of people credentialed to be teachers in the United States is something close to double the number of people currently working as teachers. What's sad is that studies of teacher competency
tend to show that the best teachers get squeezed out of the occupation the most rapidly, with lousier teachers hanging on to enjoy the job security and other nonsalary benefits. And probably at present the lack of attraction of (public sector) teaching to some job applicants results from the known low quality of many workers in that sector.