Speaking at a news conference at Sanchez Elementary School's library, Newsom said, "There's no other city in the state of California doing what we're doing, period."
Education officials say the Preschool for All program, which offers free part-day preschool to 4-year-olds, will have 4,800 slots for the city's 6,000 4-year-olds within the next few years.
"We're no longer talking about preschool as a separate entity," San Francisco Unified School District Superintendent Carlos Garcia said at the news conference. "Preschool is school."
Funding for the program came from Proposition H, which was approved by voters in 2004 and called for universal access to preschool.
The proposition authorized a charter amendment to allow an increasing portion of the city's budget to be dedicated to preschool and other education spending for 11 years, starting with $10 million in 2005-06.
In 2007, 1,700 children in certain city neighborhoods took part in the Preschool for All program and about 2,400 students from every ZIP code in the city are expected to partake this fall, according to the mayor's office.
The announcement of the Preschool for All program was made today in conjunction with the release of the city's first report to assess the readiness of San Francisco's kindergarten students.
The SFUSD partnered with First 5 San Francisco and commissioned Applied Survey Research to conduct the district-wide assessment of new kindergarten students.
Lynne Mobilio, director of research at Applied Survey Research, said at today's news conference the methodology was developed in 2000 and has been used in other Bay Area counties as well as other states.
The study used teachers' observations of children's skills, information provided by parents and a teacher survey.
Thirty teachers and 447 kindergarten students were included in the report, which found more than half of children entering kindergarten classes in the city to be well-prepared, but determined 45 percent of students need extra support, Mobilio said.
The study also indicated that children who attended preschool had an easier time transitioning into kindergarten and showed preschool can eliminate factors that contribute to low readiness scores.
The Preschool for All program provides funding to 37 public and private agencies that offer 157 classes at 89 sites throughout the city, according to the mayor's office.
Applications for the Preschool for All program can be obtained at www.first5sf.org or by calling (415) 934-4808.