Here's a legitimately scary topic never far from teachers' minds when the economy takes a downturn: the threat of being laid off.

A CALDER working paper from Katharine Strunk, Dan Goldhaber, David Knight, and Nate Brown explores the adverse impact of "pink slips" on not just teachers' mental wellbeing, but their actual classroom effectiveness.

Looking at Washington state and Los Angeles during the Great Recession, the results should make districts think twice before sending such warning notices out in advance of actually laying teachers off (and their legislatures should revisit requirements that they do so). In Los Angeles, the loss to learning for students of teachers who received a pink slip was huge—akin to the difference in effectiveness between a first-year teacher and a teacher with three or four years of experience. The findings were similarly bad in Washington.

In fact, the impact on learning in some teachers' classrooms could be measured as far as two years out from the original issue of the pink slip.

It's important to point out that some of the impact was likely not due to teachers feeling demoralized or distracted, but to the general disruption pink slips cause in school systems. Teachers often get saved from layoffs because they find a position elsewhere, and as other research has found, there is generally a negative impact on learning when teachers switch grades or schools.