U.S. President Barack Obama said in a commencement speech Saturday that race relations have improved during the past three decades, but that significant work still needs to be done. “I tell you this not to lull you into complacency but to stir you into action because there’s still so much work to do,” Obama told about 2,300 Howard University graduates in Washington.

The U.S. has a racial gap in economic opportunities, Obama said, noting that the overall unemployment rate is about 5 percent and that the comparable rate among African-Americans is almost 9 percent.

The son of a white American mother and black African father, Obama told the graduates to embrace their racial identity. “Be confident in your blackness,” the president said, adding, “There is no one way to be black … There’s no straightjacket, there’s no litmus test for authenticity.” He added that “my election did not create a postracial society.”

Obama also urged the graduates not to attempt to prod colleges and universities into disinviting controversial speakers, something that has taken place regularly at campuses throughout the U.S.

Howard University is one of about 100 historically black colleges and universities in the country.

Obama argued that the U.S. and the world have progressed dramatically since 1983 when he graduated from college. He said today’s college graduates are better positioned than any other to address big outstanding problems.

“America is by almost every measure better than it was” in 1983, the president said, noting that the U.S. poverty rate is down, the number of people with college degrees is up and the number of women in the workforce have risen.

But Obama noted an area that has not improved in recent decades: Currently at 2.2 million, the U.S. prison population has climbed significantly from 500,000 in 1983. And black men are six times more likely than white men to be incarcerated, he said. He urged the graduates to lobby the U.S. Congress to pass a pending criminal justice reform measure.