But then again, Pennsylvania requires schools to make up lost time due to teacher strikes at the end of the school year, which Canadian and Belgian schools don't. Illinois schools are required to teach 176 days a year, and the union insists that agreements to make up lost school days are traditional in bargaining agreements. But the 176-day requirement is frequently ignored, with 400,000 Chicago schoolchildren only attending school for 170 days. So there's a real possibility that the Chicago strike will end up like the Canadian and Belgian ones, with real lost instructional time and big effects on student learning as a result, rather than like the Pennsylvania one, with no lost time and no effect on learning.
One last thing: one could protest that all these results rely on standardized testing, which may or may not correlate to real learning. That's fair enough, but there's a bounty of evidence, from Harvard's Raj Chetty and Stanford's Eric Hanushek, among others, suggesting that standardized test scores correlate with higher education achievement, lifetime earnings and more. So if the Chicago strike does end up hurting student scores, it could affect their lives for years into the future.
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Matthews covers taxes, poverty, campaign finance, higher education and all things data. He has also written for The New Republic, Salon, Slate and The American Prospect.