Newsweek has a list of what it calls the 100 best high schools in America. But, my Denver readers will have to commute about 12 hours each way, every day to attend the closest one (a charter school in Tucson), and that won't leave a lot of time to actually attend classes. The reality is that K-12 education, for all but a very thin sliver of society that goes to boarding schools like Exeter (in addition to college prepartory programs, a few cater to children with special needs or disciplinary issues), is a local market.
The ranking is based on the percentage of students who take Advanced Placement and/or International Baccalaureate tests. George Washington High School in Denver, which has an IB program, might qualify as the very top (at #124 it is the second highest ranked school in the Rocky Mountain West after Lakewood High School in Lakewood, Colorado at #119), but for the fact that it has non-IB program students in the same building. Basically, it notes schools that not only have honors programs, but are honors programs, or draw from very affluent communities.
The State of Colorado, by the way, does not agree with Newsweek in its praise for George Washington High School. It calls student achievement there "average" and declining.
The truth is, that both are correct. The average student at GW is not stellar academically, but it does have an IB honors program of students who are performing very well academically. In this case (and it is not the only one in the Denver schools), the relevant microenvironment is not even a single school, it is a program within that school. Also, of course, neither Newsweek nor Colorado are measuring what really matters, which is value added. The entering class at Harvard would perform well academically even if all of the professors went on strike and the students had to teach their own classes for four years. And, even the MIT mathematics faculty would probably not bring the bulk of Manual High School's entering class up to grade level in math, although they would probably make more progress towards that goal.