Plus I suspect that there are at least some kids with a math talent who were explicitly sent to this specific school - so if you had programs like this in every school, you would probably have significantly fewer eligible candidates.
That's a contributor to how the math team continues to be successful today, but the more interesting question is how they initially became world-class ~15 years ago. Frazer is clearly responsible for the latter.
"""
Mr. Frazer’s insight was to connect four levels of education: The kids he scouts in elementary school develop in middle school, compete in high school and take specialized classes from college professors that he brings to Buchholz’s campus.
As soon as the system was in place, the team started winning and never stopped.
"""
Notice how the first step is collecting kids that are already good. The recipe is then broadly: collect the best kids you can get your hands on, train and coach them for years, watch them win. There might be some details of wider interest, but essentially this is a good old elitist project.