These lists rank whole counties against each other by their public school systems, not the schools inside them. To rank individual schools within a state, county, or city, use the school rankings; to compare districts, see the district rankings.
Counties need at least 3 schools and 1,000 students to appear. Shares are computed from raw student head counts, proficiency is enrollment-weighted and only shown where reporting schools cover most of a county's enrollment, and staffing ratios exclude special-services and vocational cooperatives, whose federally mandated staffing is not comparable.