Ed Glaeser of Harvard University provides a detailed insight on the importance of human capital for economic growth (link):
"Schools can also attract more talent with an environment that welcomes talented outsiders instead of erecting bureaucratic barriers that prevent their success. The literature on teacher certification finds few benefits from that hurdle. By contrast, Teach for America has achieved remarkable results by putting capable young people, often with little formal training as teachers, in classrooms. The experience illustrates that it isn't easy to assess teacher quality with standard teaching credentials. If attracting a wave of good people into teaching is the first step, the second step is keeping the best teachers and redirecting the rest. Performance in the classroom is the best way to know if a teacher is a success. Teacher promotion and tenure needs to be based on clear performance measures, including student test scores. Perhaps teachers unions could start endorsing the use of test scores to evaluate their members and determine tenure."