Data on college-level test participation can help determine which schools are trying hardest to energize all kids. But getting the figures from some schools can be tough. (Bill O'Leary/The Washington Post)

In my long and often unsuccessful effort to persuade high schools not to keep secrets, April 8 was a good day. Before I had to call Mamaroneck High School to ask, as I do every year, for its statistics, I saw for the first time it had posted everything I needed on its website.

Mamaroneck is the suburban New York campus where I got the idea for what is now called the America’s Most Challenging High Schools list, the 2016 version of which was recently released by The Washington Post. Twenty years ago, Mamaroneck was the scene of a book I was writing about the nation’s best public high schools. It had great teachers but a sadly narrow view of how to treat average students.

Only kids with the top grades and test scores got to take the school’s Advanced Placement courses. One ambitious junior, Kerry Constabile, was barred from the AP U.S. history course, despite her growing love for political science, because of bad marks in the ninth and 10th grades. She was so angry that she studied for the AP course on her own, getting the homework from friends, and passed the AP final exam despite getting no help from her high school.

The refusal to let some motivated students take the most challenging courses is common in many parts of the country. I invented the list to honor schools that opened those courses to anyone who wanted to work hard and to shame the majority of schools, such as Mamaroneck, where the thinking was that students not on the honor roll should have no say about the quality of their classes.

College-level test participation is the best method I have found to determine which schools are trying hardest to energize all kids. I take the number of AP, International Baccalaureate and Cambridge tests given each year and divide by the number of graduating seniors, so big schools that graduate 600 kids have no advantage over small schools that graduate just 50. Some schools fill out the forms we send them. I can also find data on the profiles posted on counseling website at schools.

But at Mamaroneck, where my book got mixed reviews, the number of AP tests, graduates and other useful numbers were not posted. Every year, I had to ask the district’s spokesman if I could please have them.

The list’s top sin, in the view of many educators, is that I rank the schools on it. The Association of Independent Schools of Greater Washington says rankings “are misleading and irrelevant to mission-oriented schools and/or detrimental to students and their families who are seeking a ‘good match’ placement.” It says “significant corrosion often results for all when even only a small number of schools participate in such practices.”

I thanked the association’s executive director, Dick Jung, for sending me those official warnings. He was the first association official in five years to return my calls or emails. But he declined to answer my questions: Does that mean you don’t believe parents are capable of looking at a ranked list in a newspaper and making their own intelligent judgment of its worth? What examples can you cite of actual harm to families and schools from rankings?

Under the Freedom of Information Act, public schools have to give me the data. The private schools can ignore me, but gradually they have been embracing the Internet-era view that useful information belongs to all. I have hopes that even Sidwell Friends, which gave my daughter a fine education, will loosen its policy of keeping secret data you would find on the profiles posted by Washington International — which has the top spot in this year’s D.C. regional rankings — and other area private schools, including Holton-Arms (No. 18), National Cathedral (No. 29) and Georgetown Visitation (No. 32).

Mamaroneck Schools Superintendent Robert Shaps told me last week that his school board’s “commitment to transparency for the community” led to the new posting of its data. He and high school Principal Elizabeth Clain have ended the bad old days of keeping students like Kerry Constabile out of AP courses — leading to a national ranking of 594, putting it in the top 3 percent. Why can’t all schools follow that excellent example?