Does seniority matter?

Well.   Kind of.   I'm not exactly sure what Valerie Strauss attempts to argue here except to say that as teachers teach more their effectiveness increases.   That's not news, although there seems to be an insinuation that Arne Duncan and Bill Gates don't believe this.     I'm pretty confident they understand this.  However, the question is not whether teachers get better as they teach more.   They do.   The question is whether or not the current system in place encourages teacher responsibility, leadership, and quality.   Or, do we have a system that is indifferent to these things.   And if it is indifferent to those qualities, is it 1) more or less likely to attract people with those characteristics or 2) more or less likely to help those already in the field develop them?