Twenty new high schools will open next year under a Bloomberg administration initiative to increase the number of specialized small schools in the city, putting the number opened in the past three years at more than 200.

Seven of the eight that already have locations are planned for the buildings of three Brooklyn high schools the Department of Education is phasing out: Samuel Tilden, South Shore, and Lafayette. A department spokeswoman, Melody Meyer, said the locations of the rest, along with two new charter schools also due to open in September, will be announced next month after a community engagement process. Five of the new schools will be transfer schools for students in danger of dropping out.

The schools chancellor, Joel Klein, said the city’s small schools have been shown to improve education offerings for traditionally underserved students. He cited a study funded by the Bill and Melinda Gates Foundation — also a backer for several small schools in the city — that was released the day of the announcement.

“The schools we’ve already created offer students personalized attention, academic rigor, and community support,” Mayor Bloomberg said in a statement.

A study released in November by the New York Immigration Coalition and Advocates for Children, two New York City-based nonprofits, found that most small schools tend to exclude immigrant and special education students, suggesting that the exclusion of high-needs students could account for the small schools’ relative success compared with larger schools.

All of the schools are required to admit a percentage of English-language learners and special education students, Ms. Meyer said, and four of the 20 new schools will offer programs for limited English students.

The teachers union president, Randi Weingarten, criticized the administration for not doing more to save the closing schools. “Sadly, the skeptics apparently were right: The DOE wanted to close Lafayette and Tilden simply to use the space to site other schools,” she said in a statement.