Macintosh Littleton has a great reputation for gifted kids. Macintosh Boulder has had some recent leadership changes and high teacher turnover. Friends School is not accelerated. Bixby is a good school and is small. Bear Creek and Superior Elementary plus Summit Charter Middle (all in the South Boulder area) are top-rated public schools, serve gifted students, and are bigger in size, but are subject to open enrollment and have long waiting lists. Peak to Peak in Lafayette is rated No. 1 for high school, but their elementary school is terrible. Stargate Charter in Thornton has the best reputation with gifted children, but again is subject to open enrollment and has long waiting lists. Westgate Charter in Northglenn is known for its 2E speciality, but has leadership issues and high teacher turnover. Douglas County and Cherry Creek are the top school districts. Douglas does very innovated things, like differentiate children by learning styles. Garland Day School in Denver is another top school, as is St Mary's Academy and Kent Day (6-12). Also, Broomfield Academy has a gifted specialty and caters to an international student body.
If you move to Boulder, stay south and stick with public schools. They are well funded and so superior to the private schools. BVSD is pretty good with gifted programming.
