After I accused American private schools of hiding vital data, a practice that makes it hard for me to compare them to other schools, National Association of Independent Schools President Patrick F. Bassett agreed to a chat. His organization represents many well-known private schools:

Mathews: You have said you don’t like my way of comparing schools. Okay, what way of comparing schools would you prefer?

Bassett: When parents ask us, “What’s the best school,” we say, “The school that best meets your child’s needs.” The first step in finding that perfect school is to evaluate what your child needs. An environment that’s more nurturing? Or more competitive? Does she thrive in a larger community or one that is smaller? Is he looking for specific classes or programs? Does the philosophy of the school mesh with your family’s values? Look at the websites and other materials from the schools. Would the approach and program at a school work for your child?

Once you have a shortlist of schools that might work, visit them. You can learn so much by observing classes and talking to teachers. Finally, talk to other parents who have kids at the school. What do they like about the school? What would they change? What made them choose the school?

Mathews: But where is the useful comparable data that can help the busy parent who does not have time to visit several campuses? You told me a decade ago you thought it would be good for independent schools to release the percentage of their graduates that have completed college. The National Student Clearinghouse now provides that data. Why don’t you urge your members to use it and report it?

Bassett: Attending, persisting, and graduating from college is indeed what independent schools are designed to prepare students to achieve. We know from data about the sector as a whole that independent schools excel in this regard. We’ll look into the National Student Clearinghouse to see whether the data it collects might be a good fit for independent schools, and, if so, recommend schools to participate.

Still, the best approach is for families, at each school they are interested in, to ask about how the school is tracking its graduates and what the results show. Many schools use the NAIS College-Age Alumni Survey, which examines graduates’ college experience, and asks them to rate how well the independent school prepared them academically and in areas such as leadership, collaboration, and fitness, among others.

Mathews: That still doesn’t explain why your members resist releasing such simple statistics as the number of AP tests given and the number of seniors graduating each year.

Bassett: If you had a website to explain your journalism work to potential clients and to keep faithful readers in the loop, would you list your weight and shoe size or highlight that you’d never worked in a pet store? Probably not, because it doesn’t help your key audiences.

Although many independent schools offer AP courses, a significant number do not. Independent schools are not obliged to follow a prescribed curriculum, but can determine independently the best way to educate students and meet their goals. Phillips Exeter Academy, for instance, doesn’t offer any AP courses. Instead, it offers classes such as American Politics and Public Policy, Molecular Genetics, and Contemporary Hispanic Theater. The Challenge Index suggests that Exeter is less concerned with challenging students than other schools because it does not offer numerous AP courses. I would beg to differ.

Tons of relevant data are available on independent schools websites, ready to mine by prospective parents desiring detailed information.

Mathews: What do you say to parents like me who don’t agree with you that that is the most important data, who think that the colleges your students get into — which often appears on your Web sites — is probably more influenced by the academic values and college pedigrees of the parents than anything the school does?

Bassett: I’d say they would be guessing instead of looking at the data.

The average SAT scores of students from all backgrounds at NAIS schools exceed the average test scores of students from other types of schools, but the margin grows significantly for students from the lowest income brackets. For students whose family incomes are less than $30,000 a year, for instance, NAIS students scored 23 percent higher on average.

Studies such as the National Education Longitudinal Study also show that low-income students who’ve attended independent schools are much more likely to succeed in college and to graduate than students from other types of schools. Why? Because these students have adjusted to the challenging academic curriculum and achievement-oriented culture of independent schools and they are well-prepared to persist and succeed in college.

This is the essence of our disagreement with your Challenge Index. Choosing a school is NOT an objective decision that can be made based on one criterion alone. It’s a subjective process that takes consideration and time.

Many people — even busy parents — spend hours researching what car to buy. Most would never think of buying a car without test-driving it… And that’s just for a car! Doesn’t it make sense to invest at least as much effort in finding the right school for one’s child?

Ranking schools is a disservice because it short-circuits the process of discovering what really counts — whether or not any individual school is a perfect match for a particular child in terms of engagement, academic programming, level of academic rigor, extracurricular offerings, etc. Rankings don’t help families narrow down or synthesize the information that matters to them; rankings trick people into thinking some criteria matter more than they should.

Here’s a question for you, Jay:

Do you have evidence that the graduates from schools high on your rankings are successful in college or life? Do they attend and graduate from college in greater numbers? Are they more likely to volunteer in their communities than students from other schools? Are the schools high on your list the best match for more students? Do Challenge Index rankings track what really counts — success in life as an engaged, productive citizen?

Mathews: Good question by you. Nobody collects data that would answer those questions either for schools on my list or schools in your association. So we have to go with what we have. (Note that automakers, unlike your members, release lots of data so that buyers can narrow down their choices before they do their test drives.)

Let’s break it down to smaller pieces. The size of a high school’s graduating class gives parents a sense of how big the high school is. If you provide the size of the ninth-grade class, they can discern how many kids stick it out all four years. But many of your schools do not report the size of either the ninth grade or the graduating class. Why not? What harm would come from revealing such a simple statistic?

Bassett: Independent schools have very little attrition — mainly from families moving away. NAIS does collect that data, but it’s of no use to the public. There is lots of room for misinterpretation too. Pundits are likely to apply a fallacious assumption: number of 9th graders - number of 12th graders = students who dropped out. That’s virtually NEVER the case for independent schools. The number of students varies year by year as a result of the school’s strategic enrollment goals (some schools admit new students in each year of high school, for instance), the number of families moving in and out of town, a family’s decision to move to another school that is a better match, student dismissal, etc. So what folks who rank schools hope for is a simple calculation that tells a story, but the calculation is never simple, and often leads to erroneous conclusions.

Independent schools do share the most important data: what students do while at the school and where graduates go to college. Matriculation to college is a clear measure of how well schools are functioning, and that’s why the best public and charter schools also share that information.