The Common Data Set (CDS) is a document with a standard format and content by which a school can post its "vital statistics" such as application and enrollment data, retention and graduation rates, test score and grade ranges, financial aid statistics, school expenditures, popularity of majors, etc. Once you get used to the format you can quickly find most of the essential "hard data" about a school, and it is usually the most up-do-date source, too, as most of the major Web data sites (like U.S. News) often lag by a year or more. Usually on a school's site you can find older CDS, too, and so see if there have been recent trends in statistics of interest.
Here, for example, is Harvard's: http://www.provost.harvard.edu/insti...n_data_set.php
-- Google "<school name> Common Data Set" and you'll probably get a hit at the top of the first page of the results.
-- Failing this, go to the school Website and search for "Common Data Set". This will often yield a hit, too, but you might have to filter out links to other research results and commentaries.
-- Failing this, search the school site for "Institutional Research" (or similar) and find the site of the school department responsible for internal monitoring. Typically Common Data Sets are there, if anywhere. You can keep an eye open for "Fact Books", too, as they often have similar data.
-- Even though by agreement they are required to make this data public, some schools simply don't post this document (WUSTL and Occidental, for example), and that is a shame, but most do comply.