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More and more school systems will be forced to lay off teachers as the full impact of the recession reaches education.  In most cases, teacher seniority will determine which teachers are let go.  While there is a fair body of research questioning this approach, a study released last week through the National Center for Analysis of Longitudinal Data in Education Research (CALDER) provides definitive evidence against this approach.

Researchers Don Boyd, Hamilton Lankford, Susanna Loeb, and James Wykoff constructed a simulation to compare the impact of a seniority based layoff to layoffs based on teacher effectiveness using live data from 4th and 5th grade teachers in New York City.  For the purposes of their study, the researchers produced a value-added measure using mathematics and English/Language Arts assessment results to estimate teacher effectiveness.  The researchers assumed a scenario in which layoffs were required to achieve a five percent reduction in expenses from salary.

Their key findings:

• Teachers laid off under the seniority policy were 0.7 standard deviations less effective than the average teacher.  
• No teachers laid off under the seniority policy received a “U” or unsatisfactory evaluation during the study period.  Using the effectiveness metric, 16% of the teachers receiving a “U” rating would have been laid off.  (I was disappointed that the alignment between the teacher evaluation system and the value-added results was not tighter).
• It required a 7% reduction in staff to meet the required budget cuts using the seniority criteria.  Only a 5% reduction in staff was required to meet the budget cuts using the effectiveness criteria.  Put another way, the layoff system based on value-added results resulted in 25% fewer layoffs.

Of course one would expect that the teachers laid off using an effectiveness metric were less competent than those laid off using seniority alone - those findings are not surprising.  What is surprising is the number of positions saved when using the effectiveness criteria instead.  Employment of the effectiveness criteria not only saved the jobs of more effective teachers, it also resulted in the layoff of fewer teachers, which ultimately preserves lower class sizes. 

This makes it hard to see how seniority based layoff policies serve either students or their teachers.  It’s quite clear that retaining the most effective teachers serves the interests of their students.  But this study also makes clear that keeping the most effective teachers better serves the interests of educators as well, since it preserves more jobs and keeps class sizes lower.  Given these findings, unions will find it more difficult to defend the position that seniority-based layoff systems serve the interests of the majority of their members.