President Barack Obama delivered a fiery assault on Mitt Romney's education policy in Nevada on Wednesday—and made a topical joke about a heckler who briefly interrupted his speech.

"That young man probably needed a good teacher. We all need it," Obama told a rowdy audience of supporters at Canyon Springs High School in Las Vegas. The crowd had drowned out the heckler with chants of "Four more years!"

Obama accused Romney of planning to cut education funding by 20 percent and said the Republican candidate views teachers as "nameless government bureaucrats that we need to cut back on." He pursued his assault on the former Massachusetts governor on the issue of school class size.

The president has been on a campaign tour targeting young voters—the same audience he will look to energize next week at stops in Iowa and Virginia. The youth vote helped propel his historic run in 2008, but young people face high unemployment in the still-sputtering economy four years later. Obama has been telling college-age crowds to make sure to register to vote.

At one point, when the crowd booed a mention of congressional Republicans, Obama responded: "Don't boo: Vote!"