The importance (or lack thereof) of certification and credentialing seems to be a popular topic these days. We have plenty of evidence that little to no difference exists (in terms of impact on student achievement scores) between teachers that are certified, have a master's degree, etc. versus those who are not. So we can conclude that certification and credentialing are ineffective, right? I heard that conclusion drawn at a presentation I recently attended, and I've read similar statements countless times in news reports and on blogs.
But hold on a minute. To say something like "certification (or credentialing) is ineffective" is a strong statement. Before you say something like this, or believe others who do, let's take a look at what we'd need to know in order to justify making such a statement.
1.) What are the purposes of certification and credentialing? Historically, I believe certification has been designed to ensure that completely unqualified people don't enter a field. For example, hiring a certified electrician means they probably won't burn your house down. I'm sure there are plenty of self-taught electricians who would do the same, but by not hiring a certified electrician you also run the risk of hiring somebody like me who would create more problems than they would solve. Many seem to assume that when somebody is certified it means they're better at it, so I think it's fair to assume -- at least based on the reaction to certification -- that it should also increase the mean quality (or at least indicate that certified workers are better than uncertified ones).
2.) How do those who completed certification and credentialing processes compare to those who didn't? This is what most people try to measure. In terms of education, they usually look at the mean value-added score for certified versus uncertified teachers, controlling for other factors. We can also examine the mean change in performance as teachers complete various credentialing processes. This partially answers the question, but we also need to know how the distribution of quality changed as a result of the process -- including whether there would be more really bad teachers if certification didn't exist.
3.) How do certification and credentialing processes change the make-up of the field? Lastly, comparisons between certified and uncertified teachers, for example, may fall short if only certain types of people are allowed to enter the field without certification (e.g. high-achieving TFA and TNTP members). In this sense, we're really answering whether certified teachers are measurably different from a select group of uncertified teachers -- not how the field would differ if we abolished certification. In the case of the latter, we might see a completely different group of people who decide to enter and remain in the field.
So before we draw any hasty and uninformed conclusions about the efficacy of teacher certification, let's make sure that we're asking and answering the right questions. We need to know both about changes in mean scores and changes in distribution of performance before we reach a conclusion. And we need to make sure we don't assume that ending certification won't change the field in ways we don't anticipate.