While truth can shine a light, it usually takes lies to generate heat.

Take the immigration debate, which is about to get underway again. President Obama has said that he intends to pursue comprehensive immigration reform. And recently, New York Senator Chuck Schumer said that he planned to have a bill written by Labor Day. We can expect six to eight months of spirited debate before Spring 2010, at which point Congress will either have passed the bill or defeated it.

Whenever we talk about immigration, much of the heat that is generated comes from myths and assumptions masquerading as facts. These are things that people know in their bones to be true, even though they aren’t really true at all. An example is when people say immigrant birthrates in the United States are going up, but all the available research points to the fact that newcomers are having smaller families — mostly for economic reasons.

Or when they say immigrants aren’t learning English when, actually, they pick it up by the second generation and have trouble retaining their native language by the third generation. Or when we say illegal immigrants don’t pay taxes when, actually, they pay their share of sales, property, and even income taxes with the help of something called an Individual Taxpayer Identification Number.

Or when they say that recent waves of immigrants — especially those from Mexico and elsewhere in Latin America — aren’t following in the footsteps of earlier immigrant waves because supposedly the newcomers aren’t assimilating to the point where their children wind up a permanent underclass because they lack wealth, skills, and education.

Again, this simply not true, according to a timely and important new study from researchers Michael J. White and Jennifer E. Glick, who examined the issue for the Russell Sage Foundation. The study -– “Achieving Anew: How New Immigrants Do in American School, Jobs, and Neighborhoods” -– torpedoes several popular misconceptions about immigrants and how they fare in U.S. society.

According to the study, the poverty gap between immigrants and natives decreased from 1994 to 2004 and the poverty level for immigrants fell over the entire decade; immigrants who arrive in the United States as children and attend U.S. schools tend to achieve parity with natives at the same socioeconomic status; and, over the generations, children of immigrants and immigrant children do as well as the children of U.S. natives unless they encounter external obstacles such as poverty or discrimination.

In fact, in a finding that some consider counterintuitive, the researchers discovered that adults born in the United States to immigrant parents were more likely to have a college degree than adults who are already in the third generation.

What’s that about? Simple. While the conventional wisdom is that the longer an immigrant family stays in the United States, the better off it will be, that’s not always the case. On the one hand, no matter what some nativists believe, assimilation happens. And when it does, immigrants are usually better off. But sometimes, what we consider progress can come at a steep price. For every new opportunity, something is lost. There are bad habits that people can pick up living in the United States for a few generations, such as a weaker work ethic, a thirst for immediate gratification, an entitlement mentality, and the tendency to take for granted the value of a college education.

So overall, immigrants are still assimilating on schedule. Some Americans think that because they see a Spanish-language billboard on the way to work, or because an ATM asks them is they’d like to proceed in Spanish, that somehow this must mean that immigrants aren’t assimilating.

No, it just means that corporations are trying to sell stuff. Hungry for a slice of an $800 billion a year market of Latino consumers, companies will use Spanish –- or French, Russian, or Martian — to help close the deal. But the important point is that these bilingual marketing efforts notwithstanding, English always finds a way to come out on top. Just as immigrants always wind up assimilating -– whether they want to or not.

That’s why studies like this are important, even if many Americans aren’t ready to accept their conclusions because the findings run contrary to what they think they know. The immigration debate already has plenty of fear, division, racism, suspicion, and animosity. What it could use more of are facts.