Magnet schools can cater to particular population (low income, minority, etc..) and gifted students too. Some big cities have public school with magnet program for gifties.

Dallas- School for gifted and Talented and and a dozen more schools
Austin- LASA for High School and 2 middle schools
Houston- Carnigie Vanguard and a few others
http://www.houstonisd.org/Page/75080

And a few more here
http://www.usnews.com/education/best-high-schools/national-rankings/magnet-school-rankings