As states revamp their teacher evaluation systems, they continue to search for that magic number: the percentage of a teacher evaluation rating that should be based on student academic performance. Here’s how this has played out over the past month:
- The Ohio State Legislature voted to lower the weighting for student growth from 50 percent of a teacher’s evaluation to 42.5 percent. Why the seemingly random choice of 42.5 percent? Because the state Senate wanted it revised downward to 35 percent and the House wanted to keep the weighting at 50 percent. Legislators compromised on 42.5 because it lies smack dab in the middle of 35 and 50.
- In New Jersey, Governor Chris Christie signed an executive order mandating that statewide exams account for 10 percent of a teacher’s evaluation this upcoming school year rather than the previously decided upon 30 percent. It will climb to 20 percent in 2015-16.
The issue here isn’t whether 10 or 35 or 50 percent is the right amount of student growth in teacher evaluations. No one knows for sure what that number is, and no one knew it when states set their initial student growth weightings either.
Ironically, we have better evidence now than we did when states made their initial decisions. The 2013 MET Project report found that weighting student growth between 33 and 50 percent of a teacher’s evaluation score would provide the best combination of predictive power and year-to-year stability. The MET Project is by no means definitive and we could certainly use more research in this realm. But before seeing any results or carrying out their own analyses, states are pre-emptively lowering their student growth weighting. And instead of using the evidence that does exist, states are allowing political battles to drive their decisions.
–Chad Aldeman and Carolyn Chuong