It's hard to say exactly how much is spent on government services for illegal immigrants, but there are several estimates. When calculating these costs, most experts include the money spent on the U.S.-born children of illegal immigrants, who are American citizens.

Here is a sampling of what studies have found:

• Education: The U.S. Supreme Court ruled in 1982 that states must provide public education to a student regardless of legal status — a cost borne mostly by state and local governments. Children of illegal immigrants make up about 6.8% of K-12 students in the United States. In California, it's at least 10%, according to the Pew Hispanic Center. Meanwhile, the Washington, D.C.-based Center for Immigration Studies, which supports stricter immigration enforcement policies, says it's 13% and that the students cost Californians roughly $9 billion a year.
• School lunches: A report by the center found that 40% of illegal immigrant households in California get food assistance, such as free school lunches, for their children.
• Health care: The center also estimates that 62% of illegal immigrants don't have health insurance and that they make up one out of four uninsured people in California. Illegal immigrants are less of a burden on the health-care system than other residents, however, because they have less access to services and tend to be younger and healthier. A study by the RAND Corporation, a nonprofit research institution, found that illegal immigrants in 2000 made up 3.2% of the U.S. population but only accounted for 1.5% of medical spending in the country.

• Incarceration: Studies have shown legal and illegal immigrants, when lumped together, are incarcerated less often than U.S.-born residents. But the federal government estimated that 12.4% of California's state prison population were illegal immigrants in 2004. Few, if any, were in prison for immigration violations. By comparison, illegal immigrants made up about 6.9% of the total California population that year.

The Fresno County Sheriff's Office says that about 10% of its inmates are illegal immigrants. A spokesman said most were there for crimes unrelated to immigration violations.

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