Roughly 10,000 children began kindergarten at public schools across San Joaquin County this year, and research being released today suggests that many of them - black and Latino children, especially - might have started school missing some of the early academic and social skills their peers already had mastered. Furthermore, they might not have had access to programs that could better prepare them.

Two reports from the nonprofit RAND Corp. examine the free preschool programs available in California and how they relate to learning gaps among the state's schoolchildren.

In San Joaquin County, and across the state as a whole, students' academic achievement varies, sometimes sharply, across different race, ethnic and income groups. Black, Latino and poor children tend to lag behind their white, Asian and wealthier peers on standardized tests of math and language-arts skills. That difference is referred to as an "achievement gap."

According to RAND researchers, a similar gap exists even among children entering kindergarten: Some children "start behind and stay behind."

Previous studies have suggested that children who go to preschool are better equipped for academic success in future school years. But RAND notes that thousands of preschool-age children in California, as many as 77,000, are not enrolled in government-subsidized early education programs that they are eligible for based on their parents' incomes. Among children who do have access to those services, some might be enrolled in programs of dubious quality with regard to child development and academic preparation.

Inside the preschool classroom at Tracy Unified's North School on Wednesday, children worked with magnetic letters, colored with chalk and created collages in small groups, each supervised by a teacher.

By March of their kindergarten year, those children will be expected to write sentences that start with a capital letter, end with a period and include spaces in between words, said Brandi Harrold, who coordinates school readiness efforts for Tracy Unified. This year, they can master more basic school skills - standing in line, following directions, learning letters.

"Then they're able to focus on the academics that we expect them to learn in kindergarten," Harrold said.

For many children without access to quality preschool programs, those academics have to be taught alongside nursery school fundamentals, which can set learning back, according to RAND.

The preschool at North maintains a low ratio of students to adults - 8-to-1. It is funded by First 5 San Joaquin, and the amount of money it receives per student goes up with the educational attainment of its teachers.

"I think we're moving in the right direction in terms of providing higher levels of quality," said Lani Schiff-Ross, program coordinator for First 5. "We don't fund baby sitters. We fund professionals."

But not all government-subsidized preschools offer such incentives to improve quality, according to the RAND research. So while nearly 260,000 children are in some type of public preschool program, they might not have the benefit of well-trained teachers, small class sizes and research-based techniques.

Miriam Coronado picked up her daughter, Daniela, from preschool at Lincoln Unified's Tully C. Knoles School on Wednesday afternoon. "Her first language is Spanish," Coronado said. "She's trying very hard to speak English. She's learning a lot. She's making sentences."

Among San Joaquin County second-graders who are learning English, only 26 percent met grade-level requirements on last spring's standardized language-arts tests. Overall among second-graders, 42 percent did.

Coronado said she believes the learning her daughter is doing this year will prepare her to succeed later on.

Like North's, the preschool Daniela attends must meet high standards for quality. By next year, teachers there will be required to have bachelor's degrees, which has been rare in the early education field.

"The more education you have, the more you understand child development and the more you can bring to the program," Knoles preschool teacher Anjie Stevenson said. "I hope this is the direction the field is going."