<p>Your hypothesis about private schools may be correct. In addition, many California public schools refrain from ranking their students. </p>
<p>But, it might also be because of this debacle: [Scripps</a> Drops in US College Rankings Due to Faulty Data ? The Student Life](<a href=“http://tsl.pomona.edu/articles/2011/9/30/news/381-scripps-drops-in-us-college-rankings-due-to-faulty-data]Scripps”>Scripps Drops in US College Rankings Due to Faulty Data - The Student Life)</p>
<p>Props to you for scouring the Common Data Set!</p>