One of the most striking arguments made against Republican governors’ efforts to curtail the bargaining rights of teachers is that it’s an “attack on the middle class.” I’m more sympathetic to that line of reasoning than you might think; for all their evils, unions have been successful in giving millions of people a path to prosperity. And, as I was reminded at my grandmother’s (a.k.a. “Nonnie’s”) funeral this past weekend, many of my second and third-generation Italian-American family members benefited from employment in public-sector, union-protected jobs.

But is it true, for teachers at least, that unions are necessary to ensure good wages? That when collective bargaining is disallowed, teacher pay plummets? I was curious, so I dug into data collected by the National Council on Teacher Quality. The group collects information on teacher pay, benefits, and much more in its tr3 database for more than 100 of the largest districts from each of the 50 states. I broke out the districts in non-collective bargaining states (those where the practice is illegal–namely, Georgia, North Carolina, South Carolina, Texas, and Virginia)–and compared them to the rest. And I looked at the maximum salary a teacher with a bachelor’s degree could earn. (See the data here.)

The surprising finding? Teachers in non-collective bargaining districts actually earn more than their union-protected peers–$64,500 on average versus $57,500. (See the chart below.)

To be sure, this isn’t a methodologically sophisticated analysis. To explore this issue further, you’d want to consider the cost of living in each locale. And ideally you’d look at more than just the largest districts. Still, this is one indication that teachers, when stripped of their right to bargain collectively, rarely get sent to the poorhouse. Or consider affluent Prince William County, Virginia, where, sans union, teachers with a bachelor’s degree manage to earn almost $90,000 per year.

On the other hand, there is some evidence from the NCTQ data that non-collective bargaining districts drive a harder bargain when it comes to health care: Just one-third of those districts offer free insurance to employees, versus one-half of those with bargaining rights. As Governor Scott Walker reminds us today, that’s what the Wisconsin fight was largely about: reining in the out-of-control costs of health care.

All of this sheds a light on what the unions are really about: protecting benefits and seniority–not pushing for higher pay. If you’re a young teacher earning a lousy salary and paying union dues, that’s something to be very angry about.

-Mike Petrilli