DEBORAH STIPEK is the dean of the Stanford University School of Education. She wrote this article for the Mercury News.

Question: What do California's prison inmates have in common, aside from having been convicted of a crime? Answer: Poor literacy skills. On average, prison inmates read at about the seventh grade level. If we had invested in their education earlier, many of them would be employed and paying taxes rather than in jail costing taxes, and our prisons would not be overflowing.

It costs more than $34,000 a year to support a prison inmate, nearly six times as much as the $6,000 a year that Proposition 82 asks to provide a child with a year of preschool. Studies have shown that children who had the advantage of a quality preschool experience are less likely to be convicted of crimes and also less likely to repeat a grade in school and to require special education services. The savings to tax payers would be far greater than the cost of preschool. Rigorous analyses by the Rand Corp. indicate that for every $1 invested in preschool we save $2 to $4 in such costs. Making high-quality preschool available to California's children is an investment in the future of our children and our state.

Proposition 82 makes quality preschool available to all 4-year-olds in California. Critics wonder why we need to provide free preschool to all children when about two-thirds of 4-year-olds are already enrolled and many parents can afford to pay for it. There are several reasons.

First, many of the programs children are currently enrolled in are of very low quality. Any policy that increased access but didn't increase quality would be a waste of money. To increase quality we need to attract talented, well-educated people into preschool teaching. To do this we need to increase the salaries of preschool teachers, which are currently lower than the average salary of janitors, and require higher levels of education. Proposition 82 does both. It also creates incentives and support for thousands of low-paid preschool teachers to get a college education, and increase their prospects as professionals. By supporting pathways to a bachelor's degree for preschool teachers, Proposition 82 will have an additional positive impact on the economic well-being of working poor families and communities.

Second, poor families are not alone in having difficulty finding quality preschools they can afford. Many middle-class families struggle to afford the $4,000 a year that a part-day preschool costs on average -- more than tuition at a California State University. Studies show that children from middle-class families benefit from preschool, and since half of all children who repeat a grade in school and half of all high school dropouts come from families in the middle 60 percent of the income ladder, investment in preschool for the middle class should produce a good return.

Third, programs targeted at the poor contribute to racial as well as economic segregation because only children from low-income families are eligible. They are also highly vulnerable to budget-cutting. California provided subsidized preschool to 82,000 children last year, far fewer than the number who are eligible. For a sense of proportion, remember that there are just over a million 3- and 4-year-olds, the age at which children usually attend preschool. According to a 2003 study of Los Angeles County, child care spaces existed for only 24 percent of the poorest one-fourth of families, and for only 29 percent of eligible children in the next fourth. A California Budget Project analysis found that 200,000 eligible children were on waiting lists for subsidized care. The real need is far greater, because waiting lists do not include the ineligible but low-income children whose families cannot afford quality preschool programs. If we want to ensure the availability of quality preschool, we need to make it a public good, something in which all Californians are invested. We already do this for 5-year-olds who attend kindergarten. Given the evidence that 4-year-old children also benefit from educational experiences, we should do it for them as well.

Despite our position as one of the wealthier states in the country, California's children are among the lowest achievers. In a test of reading skills, our fourth-graders score near the bottom compared with other states. We can make excuses for this dreadful showing -- that we have many children from families who are poor or who don't speak English at home. Or we can provide a program that helps children from those backgrounds -- and middle-class backgrounds as well -- be better prepared for success in school.

Providing high-quality preschool to all children can help us move off the bottom of the chart. If we want more of our children to develop the academic skills they will need to become working, tax-paying citizens rather than prison inmates, and if we want California to thrive economically, we need to invest in the education of the next generation. That investment needs to start with preschool.