In an intriguing piece in the current Yale Law Review, Benjamin Lindy uses the sunset of New Mexico's mandatory collective bargaining law in 1999 and its reinstatement four years later as a natural experiment, teasing out the impact of bargaining on student achievement and persistence.
The result: states with a law requiring mandatory collective bargaining see a significant increase in mean SAT scores but a decrease in graduation rates.
Lindy lays these results at the feet of transfer policies. He posits that districts engaged in bargaining are less able to move high-performing teachers to areas of high need, adhering instead to teachers' transfer requests, which typically concentrate the most effective in less challenging schools. In other words, the most at-risk students have the least effective teachers (graduation rates decrease) while those students least at-risk have the most effective teachers (SAT scores increase).
Interestingly, Lindy's model finds no significant impact (increase or decrease) on per pupil expenditures in states with mandatory collective bargaining.
We look forward to the further research this piece is certain to spark, especially confirmation of the cultural changes necessary to support Lindy's explanation that when districts make the decisions, they transfer effective teachers to where they are most needed.