Dear Extra Credit:

Your fundamental point in the Sept. 8 Extra Credit is valid and important: SAT scores tell us how much money and education the parents have, on average, and say little about how hard the school is trying to make its students better.

But your editors deserve credit for making you tee up the issue, because that's not the end of the story. Income is a confounding factor for all manner of social science research, so there has to be a remedy. And there is. It's simple and routine, and The Washington Post should push the schools to apply it.

The first step is to plot the data on a graph and add a trend line. Omitting Blair and Richard Montgomery (because of their special programs), we find that a one-point increase in the percentage of students receiving free and reduced-price meals lowers the SAT score by an average of 8.7 points. For Wheaton, the poverty effect reduces SAT scores by this: 8.7 times 38 (the percentage of low-income students), to equal 330 points. If we add those points to Wheaton's average SAT score of 881, we get a poverty-adjusted SAT score of 1211. If we compare that to the poverty-adjusted scores of other schools, we see that Wheaton is performing exactly as expected.

That would be a good first step, but it's not hard to do better. An additional indicator would be census data on the percentage of college-educated parents in a school attendance area.

Finally, it's important to realize that one-year fluctuations in SAT scores are meaningless. And once again, there is a simple remedy: report three-year moving averages instead of annual data.

Why should we bother doing any of this? The best reason is that the Montgomery County public schools should test initiatives in a small number of schools before implementing them system-wide. If an initiative raises demographically adjusted test scores, add schools to the pilot program until it is proved ready for full implementation.

John Hoven

Silver Spring

I get many smart letters like this from Montgomery County readers and sometimes hesitate to publish them for fear that my editors will realize how easy I would be to replace. I wish we followed your suggestions every time we printed the annual SAT results. I particularly like your three-year moving average idea. But I suspect that you are a man ahead of your time and that it is going take a while for us slow-witted journalists to catch up.