When I trashed private schools in a recent column because they hid their data to avoid comparison with other schools, I expected criticism. But the reaction was surprisingly friendly. I am apparently not the only past or present private school parent who rejects the widespread view among headmasters that we cannot intelligently assess comparative statistics.

The one complaint was from Washington International School head of school Clayton W. Lewis, after I ranked his school very high on my latest High School Challenge list. He sent this message to his school community:

“By their nature, ranking systems are based on minimal and inconclusive data and highlight only a small window of what a school has to offer, leaving out the particular strengths that are quite often the final determination in finding the best fit for an individual student. Because we realize choosing a school is a significant, very personal experience, we prefer individuals to develop their own ‘ranking’ based on informed research, including visits to the school.”

Lewis runs a terrific school that provides more of an academic challenge than the vast majority of public or private schools. Eventually he will realize he is too good to be consorting with private school heads who fear parents can’t be trusted with a few numbers.

One indication of that was the note sent to me by one of his school’s parents, the same one who gave me the text of his message. “I appreciate the index and hope you continue to include private schools,” she said.

Some private school insiders wondered what took me so long to identify the hidden data problem. One administrator about to become a private high school principal said he thought it was obvious. “Private schools are reticent to share their data with you because they fear losing their niche market,” he said.

The bigger issue for some readers was what they thought was my corruption of the list by adding a sampling of private schools for the first time. I rank schools by Advanced Placement and International Baccalaureate test participation rates, a way to show which are challenging even their average students. Readers pointed out including private schools violated my rule against schools that are so selective they have few or no average students.

“The private schools certainly are not going to accept kids with any history of behavioral or disciplinary problems, low admission test scores, a confirmed disability, weak teacher recommendations, below-average transcripts, perceived immaturity or who simply don’t shine during their admission interview,” Linda Arnsbarger said.

She has a point. Adding the private schools was an experiment. Next year, I will take the ultra-selective private schools off the main list and add them to the elite list designed to recognize public magnet or charter schools that are fine places to learn but have too few average students to include in this analysis.

Many private schools will still make the main list. Not all of them are highly selective. Last week I added five Catholic schools, part of the Cristo Rey Network, that recruit low-income students with an innovative program. Each student works five days a month for a local firm, usually performing office duties that develop their reading, writing and math skills. Their tuition is paid with the funds they earn on the job.

The five Cristo Rey schools on the list are in Waukegan, Ill., Boston, Lawrence, Mass., Chicago and San Francisco. They have AP participation rates in the top 9 percent or higher of U.S. schools. They prove that the disparity among private schools in the challenge of average kids is as wide as it is for public schools. Some high schools try to give all students a demanding college-level experience. Some offer that only to students with the best grades.

I wish more private schools understood the importance of challenge and were willing to report the data that reveal which kind of school they are.