In practice, separating gifted students does two things:
1. Accelerates income inequality (there's no way the gifted students on average will do poorer than the 'regular' students)
2. Remove equality of opportunity.
What exactly is a gifted school going to do that would help gifted students and not regular students?
- Small classes? Help regular students to extent.
- Better curriculum? Hey! Helps regular students.
- More practical education? Also helps regular students
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I'm not against segregation in theory. However, in practice there's very little evidence that the gifted schools would NOT benefit regular students. If you believe that gifted students should receive more education than regular students, then that's an entirely separate discussion.
If you have evidence, I'd love to see it (I'm very interested in education, in particular).