Tenure is given out to any teacher according to longevity and passing observations. That is too easy. I believe is should be given to teachers with experience and passing Praxis Observations. That is where a Praxis Field Observer comes in and observes and evaluates the teachers on a series of outcomes. ONly the highest performing teachers are then given tenure. This Praxis Observer should be used every 5 to 7 years.
Actually, there is no evidence that certification of teachers, education classes, etc. had any real effect on student learning.
Best would be comparing the test results of each teacher's students.