What about teachers who move from another state? Not all states grant reciprocity. Sometimes the new state may grant a provisional (usually 2-year) credential convertible to a regular credential if the holder gets a job within the provisional time period. Since districts avoid hiring incoming experienced teachers, the credential is likely to expire. Although not any less competent or qualified, now the teacher is even more unemployable than before.
Here is a true story: One 20-year veteran teacher moved to a new state and got the 2-year provisional credential. She began working for the district's homebound teacher program even as she continued looking for a "real" teaching job. She also worked in the education department of the local university helping undergrads earn their own teaching credentials.
Two years passed. Her credential expired. She lost her homebound teaching job because without a credential she was no longer "qualified" for the job even though she had just posted two years of highly effective experience in the very job under the supervision of the homebound program director who let her go. See the irony. The very supervisor who should have been a superior job reference let her go as "unqualified" to teach.
Even tutoring situations closed down when parents asked her if she was certified. Parents' glazed over when she would begin to explain how she was once certified, but not now. The parents took away "uncertified," a deal breaker in a society conditioned to believe that certification equals competence.
NCLB or no NCLB requirements for highly-qualified teachers, that highly qualified teacher no longer even applies for teaching jobs. When she had the credential, her masters degree and tons of experience counted against her, but at least the principal would be apologetic. Now principals dismiss her as unqualified without a second thought. She does not feel she should keep donating money to the state to continually renew a provisional credential that does not help her get a job in the face of her masters degree and experience.
With regard to master's degrees, the researchers' findings were a bit more nuanced. Teachers who had earned a master's degree before entering the field were no more effective than those without master's degrees. But teachers who got a master's degree after they began teaching were found to do a better job at boosting students' test scores than did their less-educated teaching peers.
I would guess that masters degrees earned by practicing teachers correlated with test scores because after a few years experience, teachers in the process of earning their masters degree look for specific take-aways in every class they attend. Their participation is laser-focused on acquiring immediate applications for use the very next day. They continually ask themselves, "How can I use this tomorrow?" For those going straight from the bachelors to the masters, I expect their attention is more diffused.
This study has too many flaws to be of much use, but one conclusion makes sense.
And It's possible, these researchers say, that the end-of-course exam scores used for this study may actually be a better barometer of what goes on in a classroom than the broader exams that students take in earlier grades."
End-of-course exam scores test what was actually taught. Whatever a teacher might have done effectively, an end-of-course exam would be more sensitive to that effectiveness than a standardized test.