Only 5 states do not have collective bargaining for educators and have deemed it illegal. Those states and their ranking on ACT/SAT scores are as follows:
What isn’t provided is the source of this information. There’s a reason for that and it lies in the fact that the information on test scores is from 1999!
Here is a link to the data being utilized along with a link to the main page.
Perhaps the opponents need an update when it comes to test scores.
According to the ACT website here are the states with the lowest test scores.
And from the Commonwealth Foundation is state rankings for SAT scores:
49. South Carolina
46. New York
In other words no correlation between test scores and collective bargaining rights of educators.