“Previous research on teacher strikes in Argentina, Canada, and Belgium, where work stoppages lasted much longer, found large negative effects on student achievement from teacher strikes. (In the Argentina study, the average student lost 88 school days.)
In contrast, the researchers find no evidence that US teacher strikes, which are much shorter, affected reading or math achievement for students in the year of the strike, or in the five years after. While US strikes lasting two or more weeks negatively affected math achievement in both the year of the strike and the year after, scores rebounded for students after that.
In fact, Lyon said they could not rule out that the brief teacher strikes actually boosted student learning over time, given the increased school spending associated with them. A recent influential meta-analysis on school finance found that increasing operational spending by $1,000 per student for four years helped student learning.
It’s possible higher wages could reduce teacher burnout, or the need to work second jobs, leading to improved performance in the classroom. Still, Lyon explained, it’s also possible that increased spending on teachers would not lead to higher student test scores, if wage gains went primarily to more experienced teachers, or to pensions, or if teachers were already maximizing their effort before the strike.”
https://www.vox.com/education/368756/teachers-school-unions-labor-education-students-strikes