Because of a brilliant media campaign by charter school organizations, there is a widespread impression that any charter school is better than any public school. This is not true. Charter schools vary in quality from excellent to abysmal. On the authoritative federal tests called the National Assessment of Educational Progress, students in charter schools perform about the same as those in traditional public schools. A recent Stanford University study, which compared half the nation's charter schools with a neighboring public school, concluded that 46 percent were no better, 37 percent were significantly worse and only 17 percent were significantly better than the public school. Philadelphia launched an effort last year to compare its district-run schools with its charter schools and privately managed schools. Researchers from Rand Corp. concluded that charter students did no better than those who attended public schools. Performance in the privately managed schools did not, on average, exceed the performance of the public schools. A few months ago, Philadelphia officials -- looking at their own achievement data -- said that six privately managed elementary and middle schools outperformed the public schools, but 10 were worse than district-run schools. One of the major arguments for turning schools over to private managers is that the resulting competition will spur improvements in public schools. This did not happen in Philadelphia, nor is there evidence that it has happened elsewhere. Many charter and privately managed schools get extra resources and smaller classes with the help of corporate sponsors, but public schools typically do not. What the public schools do get are the low-performing and disruptive students who are ejected by or eased out of the charter and privately managed schools. The Los Angeles proposal for 50 new schools has been likened to New York City's approach. But Los Angeles should be aware of two points. First, under New York Mayor Michael Bloomberg, spending on education has increased from $12.5 billion annually to $21 billion, or nearly $20,000 per child. Is Los Angeles willing to match that? Second, New York City's new high schools started small and were allowed to limit the admission of special-education students and students with limited English proficiency for the first two years. The remaining high schools were left with a disproportionate share of the neediest students. A study this year of the new schools found that, over time, when their enrollment became similar to traditional public schools, their attendance rates and graduation rates declined. Also, the attrition rate of teachers and principals was consistently high. If we are ever going to get serious about improving education in the United States, we have to face up to basic facts. We can't solve our problems by handing them off to businesses and community groups. Some schools will claim success by excluding the students who are hardest to educate; others will claim success by drilling children endlessly on test-taking skills. And although California law requires that public schools -- charters included -- accept all students, charters tend to draw the most motivated students and families away from the traditional public schools because of the application process. Further, charters and privately managed schools often pay unusually high executive compensation. The leader of a small charter network in New York City that has 1,000 students received $370,000 in 2007, about triple the salary of a principal. The organizer of charter schools in a Pennsylvania suburb is also the primary vendor of goods and services to his schools and earns more than $1 million annually. What should we do? We must strengthen -- not abandon -- public education. Our schools should have well-rounded curricula that include the arts, history, science, geography, literature and foreign languages, as well as basic skills. Teachers should be well-educated and treated with dignity. Principals should be head teachers, who can capably evaluate and assist their teachers. School buildings should be well-maintained. Class sizes should be reasonable, making it possible for teachers to give extra attention to students who need it. Schools should have a firm and fair disciplinary code. Are these common-sense policies beyond the reach of the citizens of Los Angeles? We evade our responsibility to improve public education by privatizing public schools. In doing so, we undermine the egalitarian promise of public education, thus guaranteeing that many children will continue to be left behind. Ravitch is a historian of education at New York University; her new book, 'The Death and Life of the Great American School System,' will be published in March. 