At The Quick and the Ed, Chad Aldeman says districts should change the way they pay teachers to reflect "that the vast majority of teaching improvement comes in the first few years on the job." He pulls up some nice charts and graphs showing how teachers' impact on student test scores does up steadily over their first few years of teaching, then levels off for the rest of their careers.
YES, BUT — Do some veteran teachers contribute value in addition to student test scores? An effective teacher in her 15th year might contribute significantly more than an effective teacher in his 4th year in terms of mentoring/ developing other teachers, writing curriculum, helping shape school policies, collecting school resources, etc. All of these factors are key in a well-run system, and all contribute to the in-class effectiveness of that 4th year teacher.
As a 3rd year teacher who is relatively effective in terms of student test scores, I know anecdotally that my more experienced colleagues contribute much more than I do to the school as a whole. Veteran colleagues in my school share lesson and unit plans, organize school-wide collections of student learning materials, plan joint field trips, help guide school policy, and advise me on tough teaching decisions. They don't get paid or particularly lauded for any of that; they do it because it's a way to contribute to more students once they've gotten pretty good at teaching their own students. I would love to do that stuff too, but as a newer teacher, I'm just not there yet. Soon. I hope.
To be sure, not all veteran teachers contribute in these ways, but many do, and maybe all should. DC's IMPACT evaluations have some room for this kind of school-level contribution -- maybe that school contribution box should be bigger?