The Washington Post’s (formerly Newsweek’s) annual rankings of the most challenging U.S. high schools come out in the spring with an addition I thought I would never see: private schools. I think this will help parents who wonder whether public or private schools would be better for their children.

When I started the Challenge Index in Newsweek in 1998, the headmasters and headmistresses of our nation’s tuition-charging high schools reacted as though I had invited them to a strip joint. They were offended. The National Association of Independent Schools warned members to stay away from me and my threatening effort to give parents data that private schools had hidden for years.

They said my list was a blatantly commercial exercise, designed only to raise circulation. They said it appealed to an unfortunate consumer mentality among parents. They said applicants and their families should decide on schools by visiting their campuses and talking to their students. They said their schools could not be defined by a number. They implied that demanding quantitative information on how many of their students were getting an authentic college experience was gauche.

I rarely get those complaints anymore. The list has become a springtime ritual for public high schools. Principals tell me it helps them see whether they are preparing the maximum number of students for higher education. Parents say they that know it is just one factor in judging a school but that they appreciate the chance to compare one school to another on the same scale.

More than 2,000 public schools were ranked last year. I include on the national list only schools that rank in the top 10 percent nationally, but my annual local list in The Post rates every public high school in the Washington area.

Many schools that I have missed on my database ask that I include them. In recent years, several of those requests have come from private schools. They say it helps their parents, and they don’t feel they are at a competitive disadvantage giving out the data. Many Catholic schools that have large numbers of low-income students want to show outsiders what they are doing to prepare some disadvantaged students for college.

My analysis of data I have received from private schools indicates that their college-level test participation rate — what the Challenge Index measures — is similar to that of public schools with similar mixes of students. Some private schools, however, surprise me. St. Anselm’s Abbey School, a tiny campus in Northeast Washington not nearly as well known as St. Albans or Sidwell Friends, has for many years had Advanced Placement test participation rates far above those of more famous schools. Its ratio last year of 7.25 AP tests for every graduating senior would have made it No. 1 in the Washington area and 27th in the country if I had included private schools on the list.

So, in the spring, I am going to do just that. If you work at or have a child attending a private school anywhere in the nation with a strong AP, International Baccalaureate or Advanced International Certificate of Education program, urge the principal to send his or her e-mail address to me at I will send the online form to fill out.

I will list every private school, probably with a (P) next to the school name, whose ratio of college-level tests to graduating seniors reaches our target, 1.000 or larger. If the school is in the Washington area, I will put it on the local list no matter its ratio.

The more private schools that participate, the better. We all have our own impressions of the difference between public and private. But this spring, take a look. You might be surprised.