My former school district (Virginia Beach) has an elementary magnet school and a middle school exlusively for gifted. All children were eligible for gifted clustering in ES and MS in their 'home schools', but your child could apply to one of these schools if they tested gifted... and these schools were highly selective and the programs very rigorous compared to taking say an accelerated track in your assigned MS. The IB program was also offered in MS and HS and though giftedness was not a requirement, the program was highly selective academically. The school district also had a number of 'schools within schools' at the high school level in different disciplines like math, technology, language, etc.
