Talks between the Chicago Public Schools and the Chicago Teachers Union broke down Sunday, and now the city's teachers are on strike, just as classes were starting for the 2012-13 school year. Labor will insist that the strikes lead to contracts that attract good teachers who promote student learning in the long-run. Mayor Rahm Emanuel, meanwhile, notes that the teachers are striking over his proposed evaluation system, which he argues will help achievement going forward. Leaving that debate aside, what does the strike itself mean for students?
Nothing good, the best empirical evidence suggests. Two of the best recent studies on the effects of teacher work stoppages and strikes concern labor disputes in Ontario schools in the late '90s and early 2000s. One, by the University of Toronto's Michael Baker, compared how standardized test scores rose between grade 3 and grade 6 for students who lost instructional time because of the Ontario strikes, and for students who were unaffected.
Baker found that if the strike happened when a student was in grade 2 or 3, their scores rose by slightly less. But if the strike happened when the student was in grade 5 or 6, their scores rose by a whole lot less. Scores for strike-affected fifth-graders were a full 3.8 percent lower than those for fifth-graders in schools and grades not affected. If that doesn't seem like much, it's 29 percent of the standard deviation (or the typical amount by which students differ from their class average). Strikes, in other words, accounted for one third of why some students did better than others.
Wilfrid Laurer's David Johnson studied the same Ontario strikes and also found that they hurt student achievement. Like Baker, he found only small effects for students for whom the strike occurred in third grade, but large effects if the student was in sixth grade. In the latter case, the percentage of students getting a passing score on math standardized tests fell by 0.21 percentage points per day, and the percentage getting a non-failing score across all tests fell by 0.10 points per day. The effects were much more dramatic in poorer and more socially disadvantaged school districts, where overall passing scores went down by 0.35 points per day. Given that strikes typically last a week or more, these results can add up. A nine-day strike, for instance, reduces passing rates 3.15 percentage points.