In the 1990's, conditions in Mexico produced a flood of illegal immigrants to the United States. Harsh new state laws, tougher border enforcement and criminal gangs make crossing into the US without papers a lot harder than it used to be. But 90 percent of the Mexicans who want to cross illegally can actually make it. So why has the flood of illegal immigrants been reduced to a trickle? The biggest reason is education, producing more children with greater skills than their parents. With investment creating new jobs, they want to stay home. Mexico has by no means solved all its problems, but it's changing fast — with not just one, but two middle classes. We hear what it all means for the US.