Since President Obama’s daughter Malia attends the Sidwell Friends Upper School and her Sidwell Middle School sister Sasha will too, I would argue it is our most famous private high school.

Sidwell has many great teachers and splendid facilities on a lovely campus stretching out along the 3800 block of Wisconsin Ave. in Northwest. Tuition is $36,264, but applications pour in.

So why, with all that fame and success, is Sidwell so reluctant to release any data on how its students are doing? Other private schools, such as Washington International, National Cathedral and Gonzaga, reveal on their Web sites how many students graduate, the number of and passing rates on Advanced Placement and International Baccalaureate exams, and SAT and ACT test score averages.

Sidwell keeps that data secret. The numbers could help parents and potential applicants, but they also could be used to compare Sidwell to other schools. Sidwell and some other local private schools resist being part of any ranked list, including the America’s Most Challenging High Schools survey I do every year for The Washington Post.

“We believe that parents and students are not helped by rating systems which purport to evaluate school quality based on test data,” Sidwell head of school Tom Farquhar told me. Independent Education, the local private school association, encourages all of its members to keep their numbers to themselves.

Farquhar acknowledged that the fear of being compared to other schools is at odds with what many private educators see as their responsibility to their parents and potential applicants, leading some Independent Education members — but not Sidwell — to put the information out anyway. “They are proud of how well their kids are doing and they are comfortable with prospective families taking a look at all the available information as they weigh their decision,” he said.

I have been ranking public high schools, locally and nationally, since 1998. I don’t rate schools by test scores because that is more a measure of parental affluence than educational quality. I instead report the rate of participation in college-level exams, particularly AP, IB and the Advanced International Certificate of Education. The ratio of college-level exams to graduating class size indicates which schools work hard to get all students ready for college rather than restricting AP and IB to those with the highest grades.

Public schools are required, because of freedom of information laws, to give me their data. Private schools are not. When I began adding private schools to the list in 2012, I could provide only a sampling because some, like Sidwell, Georgetown Day and St. Albans, do not release their data to potential applicants, or to me. But the information I have indicates that some private schools are less likely than others to expose students to courses and tests that give high school students a real taste of what college will demand.

The highest-ranking Washington area private schools on my 2014 list are St. Anselm’s Abbey, with a ratio of 7.61, and Washington International, with a ratio of 7.31. Maret’s ratio is 2.93. Maret’s spokeswoman told me the school had not meant to put its AP data on its Web site and would not do so again. They can tell those who complain that they are just doing what the famous Sidwell does.

I know Sidwell well. It gave my daughter a fine education. We still donate to the school. But its Web site could use more information and less press agent prose, such as statements extolling the school’s “joyful environment.” Like other schools with many ambitious students, its teenagers don’t feel that their days are full of joy.

The most famous private colleges don’t hide their data, even though they also don’t like to be ranked. Our most famous private high schools should follow their example.