Newsweek published its annual list of the top 1,500 public high schools in the country this week. Iowa has six schools on the list: Cedar Rapids Washington (number 477), Cedar Rapids Kennedy (732), Iowa City West (846), Ames (923), West Des Moines Valley (1389), and Mid-Prairie of Wellman (1468).

A simple formula determined the rankings:

Public schools are ranked according to a ratio devised by Jay Mathews: the number of Advanced Placement, Intl. Baccalaureate and/or Cambridge tests taken by all students at a school in 2008 divided by the number of graduating seniors. All of the schools on the list have an index of at least 1.000; they are in the top 6 percent of public schools measured this way.

Note that this formula doesn’t tell you how well each school’s students did on the tests; it merely indicates how broad a segment of the school’s population is being prepared for college-level work. It also doesn’t give you any sense of other qualities in a high school, such as the range of extracurricular activities available.

Still, it’s important for high schools to prepare kids for college. Congratulations to the Iowa school districts that make advanced work available to a large percentage of students, especially in a small town like Wellman (population under 1,500 in Washington County).

Selective schools such as magnets and charters dominate the top of Newsweek’s list. While these are technically public schools, they are not comparable to schools that accept all students living within certain geographic boundaries. Most of the highest-ranked schools are in metropolitan areas larger than any Iowa city.

On the other hand, the fact that only one Iowa school cracked the top 500 on this list is a wake-up call to Iowans who consider our public schools the best in the country.

Speaking of Advanced Placement courses, Rachael Giertz had a good letter to the editor of the Des Moines Register a few weeks ago. It’s not still available on the Register’s website, but Giertz mentioned one downside for students who pile up AP credits in high school. Those credits help students finish college faster, but they may not count as courses passed on graduate school applications. Many graduate schools (rightly, in my opinion) don’t consider an AP course passed in high school equivalent to the same course taken in college.