As we frequently like to point out here at The Atlantic, going to college is perhaps the single best financial decision a young adult can make. But there's a catch: you have to graduate. If not, the costs can easily swamp the benefits.

And that is one of the most important reasons why, in many ways, America's higher education system does more to deepen class divisions than it does to bridge them. Because the truth is that compared to their richer classmates, low-income students have only a faint hope of ever graduating from college if they even get there.

The two graphs below, from a recent report by Third Way, and based on major longitudinal studies of American youth, show how wide that gulf is. The blue dotted line tracks the youngest Baby Boomers, while the red line looks at the oldest Millennials. First, note that between the generations, the rich-poor attendance gap grew from 39 percentage points to 51 percentage points.

But graduation rates are perhaps even more appalling. Just 9 percent of students from the poorest families complete a degree -- meaning less than a third who ever enroll make it to commencement. By comparison, 54 percent of the most wealthy students earn a diploma, meaning they have about a two-thirds success rate.

Poor preparation may play a role here, but so do finances. Many low income students attempt to work their way through school without debt, which puts them at a greater risk of dropping out. Others find themselves financially overwhelmed even with the help of loans. Bottom line: For Americans of a certain class, college is a basic rite of passage. For many more, it's a roll of the dice.