According to a new survey conducted by Airbnb, 10 percent of the company’s hosts in the United States are teachers. That’s pretty remarkable given that less than 2 percent of the country are K-12 educators. So what’s driving teachers to rent out their homes and spare bedrooms? It’s obvious: low pay.

A new analysis from the Economic Policy Institute finds that public school teachers are paid on average nearly 20 percent less than workers in professions that require similar education and training. The researchers also found that in 1994 the pay gap was roughly 2 percent — meaning the “wage penalty” that public school teachers face for electing to educate our nation’s children has risen by 18 percentage points in just a couple of decades.

It’s not just the comparison to other professions that’s dismal. The report finds that, adjusted for inflation, teacher pay has actually decreased since the mid-90s. Meanwhile costs of living have skyrocketed, and each dollar buys less than it did twenty years ago. Many teachers are desperate for ways to make up the difference.