The massive gap in college graduation rates between rich and and poor is growing even wider.

Some 77% of students from wealthy families earned bachelor's degrees by age 24 in 2013, compared to only 9% of those from poor families, a new report has found.

That divide has grown significantly from 1970, when 40% of rich students and 6% of poor ones graduated college, according to the report from The Pell Institute and the Alliance for Higher Education and Democracy at the University of Pennsylvania.

The study defines the wealthy as having family incomes above $108,650, while the poor earned less than $34,160.

Middle class students also lag behind their better-off peers. Those in the middle saw their graduation rates rise to only 26% in 2013, up from 13% in 1970.

Related: The growing poverty problem in America's schools

This gap in college graduation rates between rich and poor is contributing to the "growing divide between the 'haves' and the 'have-nots,'" the report said.

Those with college degrees tend to have higher earnings, lower unemployment rates and poverty levels, better health and longer lives. Society as a whole also benefits from higher graduation rates since the tax base increases and dependence on government assistance decreases.

President Obama has tried to address this contributor to income inequality by increasing access to college. Among his latest proposals is making community college free.

Related: Obama wants community college to be free

A small bit of good news: More high school graduates from poor families are going to college. The rate shot up to 62% in 2012, up from 46% in 1970. Among the wealthy, nearly nine in 10 go to college, up from eight in 10 in 1970.

But not that many of those poor students entering college are leaving with degrees, while nearly every rich one is. Only 21% received bachelors by age 24, compared to 99% of their wealthier peers. This gap has grown dramatically since 1970, when 22% of poor students graduated but only 55% of rich ones did.