In 1998, while trying to draw attention to a book I had written, I created a ranked list of the most demanding U.S. high schools. I called it the Challenge Index. It was a publicity stunt, a peculiar approach to school assessment I didn’t think would last very long.

I took the number of Advanced Placement or International Baccalaureate exams taken by all students at each school and divided that by the number of seniors who graduated that year. The ratio showed which public schools were working hardest to get average students to take those college-level courses and exams. I had seen great teachers at a few schools reveal the potential of overlooked kids by challenging them that way. Why not report what other schools were doing?

My book sold poorly. But I was surprised at the positive reaction to my list from ambitious teachers, principals and parents when Newsweek published it. Educators thanked me for spotlighting their efforts to change students’ lives. Newsweek made it an annual event. Eventually I moved the list to The Washington Post and then to my own website, jaymathewschallengeindex.com.

Some people said it was crazy to judge a school by just one number. I pointed out that was nothing new. Many affluent schools based their reputations on their high SAT or ACT score average. That was not assessing them by how well they taught, but by how rich and well-educated their students’ parents were. My college-level-exam participation rate revealed which schools were trying to give deep teaching to as many kids as possible — even C students. That was rare in the easy-does-it American high school system, but the schools that ranked high on the list included some with mostly impoverished kids.

There will be no Challenge Index list next year. I will not have enough meaningful data because of the disruption of this year’s AP, IB and Cambridge programs by the coronavirus pandemic. Hopefully those traditional college-level tests will be back next year and I can publish a list in 2022.

I confess I have become addicted to the process. I think it makes valid points. It keeps me in touch with thousands of smart educators across the country. And surely you won’t deny an old guy his favorite hobby.

One thing I have noticed, looking back on all that data, is that the schools on the top of the first list in 1998 were almost entirely different from the top schools this year, based on 2019 data. When it comes to preparing average high school students for college, there has been a remarkable change in the past 22 years.

In 1998, the top 20 on the list consisted of 16 neighborhood schools in affluent communities and four magnets that attracted some of the best students. The magnets in that group were Stanton College Prep in Jacksonville, Fla., Richard Montgomery in Rockville, Md., H-B Woodlawn in Arlington, Va., and North Hollywood in North Hollywood, Calif.

I excluded some of the most famous magnets, such as the Thomas Jefferson High School for Science and Technology in Fairfax County, Va., because they were too selective for a list designed to show which schools challenged average students. If their average SAT or ACT scores were above those of the neighborhood schools with the highest averages, they were put on a special Public Elites list.

This year, the top 20 consist of 14 public charter schools and six magnets. I added private schools in 2012, but none of them ranked that high this year. The affluent neighborhood public schools that dominated the list in 1998 have fallen behind. That is interesting and somewhat encouraging, given that seven of those charters (all of them part of the IDEA Public Schools charter network in Texas) have student populations that are at least 75 percent low-income. The magnets include Carnegie Vanguard in Houston, Downingtown STEM Academy in Downingtown, Pa., the Marine Academy of Science and Technology at Florida International University in North Miami, Jefferson County IB in Irondale, Ala., and Suncoast Community in Riviera Beach, Fla.

The Jacksonville magnet Stanton College Prep is also there, the only school to be in the top 20 in both 1998 and 2020. Stanton offers both AP and IB courses. About 23 percent of its students are Black or Hispanic, compared with only 4 percent at the nation’s most selective magnet, Jefferson. Stanton has increased its ratio of the number of college-level exams to the number of graduating seniors from 4.090 to 16.308 in those 22 years.

The rise of previously unsung schools involving even average students in college-level courses is not the result of government programs or national initiatives. The movement has been led by mere local educators who believe ordinary teenagers are capable of learning much more than they are usually taught.

The portion of schools who qualify for the list, by giving at least as many college-level exams as they have graduating seniors, has increased from 1 percent in 1998 to 12 percent in 2019. That’s steady progress. But to get on the list, a school only has to have half of its 11th- and 12th-graders each take just one AP, IB or Cambridge International test. The 88 percent of schools that haven’t reached that level should start thinking, after they recover from the pandemic, why they cannot do at least as well.