David Hills/The Heritage Foundation

ABC News' Sarah Parnass and Shushannah Walshe report:

Jason Richwine, the co-author of a controversial report on immigration released this week, has resigned from the Heritage Foundation.

"Jason Richwine let us know he's decided to resign from his position," read a statement from the Heritage Foundation released Friday afternoon. "He's no longer employed by Heritage."

The statement added that it was the Heritage Foundation's "long-standing policy not to discuss internal personnel matters."

Richwine and The Heritage Foundation were the subject of criticism earlier this week when they released a report that put a $6.3 trillion price tag on immigration reform. Then, Richwine came under fire because of prior arguments he made about race.

Richwine argued both in his dissertation for Harvard in 2009 and in a forum at the American Enterprise Institute in 2008 that Hispanics and blacks are intellectually inferior to whites and have trouble assimilating because of a supposed genetic predisposition to lower IQ. He said that this made current-day Hispanic immigrants less equipped to adapt to life in America than the largely European immigrants of the late 19th and early 20th centuries.

"We have blacks, we have American Indians and even early Mexican Americans who have been living in the country for a long time and have not assimilated to the cultural mainstream as typified by white Americans," Richwine told the panel in 2008, four months before the first African-American president was elected.

"These are real differences. They're not going to go away tomorrow, and for that reason we have to address them in our immigration discussions or debates," he said.

While some continue to embrace the purported connection between race and IQ, others argue IQ is an inaccurate measure of intelligence and race cannot be scientifically defined.

The study put together by Richwine and Robert Rector, the man behind the Mitt Romney ad that accused President Obama of gutting welfare, argued that the immigration proposal put forward by the Senate's bipartisan, so-called Gang of Eight would cost taxpayers $6.3 trillion. That whopping number was based on their analysis that showed immigrants that came to the country illegally tended to have only some high school education, and that households with lower education consume more from the government than they pay in taxes.

"The benefits received by unlawful and low-skill immigrant households exceed taxes paid at each age level; at no point do these households pay more in taxes than they receive in benefits," the study read. "In general, government policy should limit immigration to those who will be net fiscal contributors, avoiding those who will increase poverty and impose new costs on overburdened U.S. taxpayers."

A Pew Research Center poll released this week showed Hispanic students graduating in the class of 2012 were more likely than their white peers to go on to college.

"In October 2012, 66 [percent] of all recent high school completers were enrolled in college," the study said. "Among Hispanics who had recently graduated high school, 69 [percent] were enrolled."

The report said the increase in Hispanic students choosing to go on to college might be attributable to the lack of jobs available since the recession.

"Another factor, however, could be the importance that Latino families place on a college education," the study said. "According to a 2009 Pew Hispanic Center survey, 88 percent of Latinos ages 16 and older agreed that a college degree is necessary to get ahead in life today."