Two weeks before the start of the final full school year of his mayoralty, Mr. Bloomberg seized the opportunity to call on legislators in Albany to renew the law, which expires in June, giving New York City’s mayor control of its school system. Debate is expected to begin this fall on whether to extend the law or amend it, placing checks, for example, on the mayor’s authority.  “You can’t run something this big without having one person have accountability,” Mr. Bloomberg said of the school system. “That’s what the Legislature gave us, and hopefully come next June, they will reapprove and make permanent the change. And if they try to water it down, they might as well just take it away. Either you have accountability or you don’t.”  The city’s charter schools generally outperform traditional public schools on standardized reading and math tests, and many charters have been flooded with applications and have had to turn away hundreds of children whose names are not drawn in admissions lotteries. But charters have not been universally embraced. In some places, parents have complained about the mayor’s policy of giving charter schools space in existing public school buildings and about the unfairness of their smaller class size, and have called them a diversion from his responsibility to fix the school system overall.  Charter schools have also drawn criticism from the powerful United Federation of Teachers, the city’s teachers’ union, because the vast majority are not unionized. In an effort to show that the success of a charter school does not hinge on its freedom from a union contract, the union itself now runs two charters, and one of the 18 new schools Mayor Bloomberg announced will also be unionized. That one, the Green Dot New York Charter School, is run by an organization with a network of charters in Los Angeles.  Charter-school supporters are deeply concerned that whoever succeeds Mr. Bloomberg in 2010 might lack his enthusiasm for them. The mayor said on Monday that he had tried to make New York “the most charter-friendly city in all of America.”  A version of this article appears in print on , on Page B2 of the New York edition with the headline: 18 New Charter Schools To Open in September, Bloomberg Announces. Order Reprints| Today's Paper|Subscribe
The new schools — the largest number to open in the city in a single year — will bring the number of charter schools in the city to 78, serving 24,000 students.