In 1986, Congress passed the Immigration Reform and Control Act, a piece of legislation granting legal status to undocumented immigrants in the United States that was both more sweeping in ambition and smaller in scale than Barack Obama's executive action last week. The bill was more ambitious in that it sought to create a definitive solution to immigration (that, obviously, did not pan out). It was smaller in scale in that it ultimately touched fewer immigrants than Obama's action could today.

Three million undocumented immigrants applied for legal status under IRCA. Ultimately, about 2.7 million received it. Because the bill required immigrants to have entered the country prior to 1982, beneficiaries of that amnesty who have stayed in the U.S. have now been here more than three decades. Their lives, in short, could reveal a lot about the long-term and inter-generational consequences of legalization.

So what do we know about what happened to that earlier wave of immigrants? Only a little bit -- and hardly enough to measure the impact of a massive government policy change. The Department of Labor sponsored two survey studies following up on several thousand of the IRCA immigrants -- in 1989 and then again in 1992, five years after the law went into effect.

Those studies suggested that immigrants made significant wage gains in the years after legalization, many of them by obtaining better jobs. Government records also revealed over time how many of them became naturalized citizens. In 1996, the year the entire IRCA cohort was eligible, a quarter of a million were naturalized. By 2001, one-third of the entire group had been.

These naturalization rates  suggest that many immigrants may not have been looking for citizenship so much as economic stability. That trend, too, is in keeping with what many immigrants say of their long-term intentions.

"When you talk to immigrants, many of them say that they plan in the long run to return home, to retire back to Mexico, to Central America," says Marc Rosenblum, the deputy director of the U.S. Immigration Program at the Migration Policy Institute. "They’re looking for short-term security."

Mexican immigrants under IRCA were also the least likely to seek citizenship, mirroring a long-term pattern. Being closer to home, Rosenblum suggests, may make it feel easier to go back. Until the late 1990s, Mexico also didn't offer dual citizenship.

Beyond the 1992 study, though, there is no survey data tracking how the following years unfolded. And there's similarly little known about the prospects over time of two smaller waves of immigrants granted reprieves -- in an effort to patch IRCA -- by Reagan and George H.W. Bush.

"That means that we don’t know a lot about some of the things like how their children have fared, their participation in the political process, other non-economic indicators of well-being and integration and health," Rosenblum says. "There’s a whole long list of things that we don’t really know, especially over time."

There's reason to suspect, however, that giving an immigrant legal status might impact much more than his or her job prospects. "There’s stress associated with the fear of deportation that would be reduced," Rosenblum says. And that implies that immigrants might have better health outcomes once that fear is removed — just as they'd have better outcomes thanks to access to health insurance that comes with better jobs.

Other research suggests that children of undocumented immigrants are more likely to be poor and in poor health than children of legal parents. And so we might reasonably expect the children of immigrants to benefit from their legal status, too — even if they're not born until well after any amnesty is granted.

And then there are many more questions: Are immigrants more likely to invest in education, or community institutions, or political participation once they have legal status? Do they become more likely to learn English? Do their children become more likely to go to college, or to experience upward mobility?

Immigrant communities are often less likely to report crimes or cooperate with law enforcement, for fear of deportation, or of exposing friends and family who are undocumented. So what might happen to crime reporting and community policing after a wave of legalization?

We also don't know a lot about what happens to the jobs they leave as they move on to better work, or their impact on the wages of other workers, or on the finances of the communities where they live.

Obama last week did not extend the same offer that Congress did in 1986. He promised a temporary answer -- deferred deportations for as many as 5 million undocumented immigrants -- not a permanent path to citizenship. And so it's likely that the consequences for families now will look different, too. But it's also possible that we could be having a different conversation this time around about immigration reform if we better knew how much it benefited families and communities and tax coffers the last time.

What if we knew, for instance, that children whose parents were granted legal status were less likely to have diabetes? Or that undocumented day laborers were more likely to become licensed electricians? Or that parents were more likely to join the PTA if they became legalized residents?