There is a growing divide between those who earn a bachelor’s degree by age 24 and those who don’t, with the gap between the richest and poorest students doubling in the last four decades, according to a report released Tuesday.
The percentage of students from the lowest-income families — those making $34,160 a year or less — earning a bachelor’s degree inched up just three points from 1970 to 2013, rising to 9 percent from 6 percent.
College completion for students from the wealthiest families rose dramatically, though, climbing to 77 percent from 44 percent.
‘‘It’s really quite amazing how big the differences have become between those from the highest and lowest family incomes,’’ said Laura Perna, a University of Pennsylvania professor and executive director of the Alliance for Higher Education and Democracy, one of two organizations that published the study.
It comes amid renewed debate on college affordability spurred by President Obama’s proposal to make two years of college free. If adopted in every state, the plan would benefit a projected 9 million students a year. It would cost taxpayers an estimated $60 billion over 10 years — a price the Republican-controlled Congress is likely to be hesitant to embrace.
The widening gap in college completion mirrors a growing divide in income inequality: While pay for the richest 10 percent of the nation has jumped in recent decades, for most Americans it has stagnated, after accounting for inflation.