By the time the children of illegal immigrants reach age 2, they show significantly lower levels of language and cognitive development than the children of legal immigrants and native-born parents

This should not be too surprising since illegal immigrants - such as Mexicans and other Latinos - tend to be from the poorer, less intelligent segments of their native countries. Poor cognitive development can lead to lower school performance, which in turn can lead to higher dropout rates, an under-trained work force and lower economic productivity.