Sierra Magazine has released its annual “Cool Schools” environmental rankings of U.S. colleges and universities. Their rating appears to be just that—an assessment of the school’s green hip factor. At least, that’s what I’m left to guess. The magazine based its ratings on questionnaires sent to the schools and doesn’t disclose many details about how it evaluated the answers.

A comparison of the top 10 rankings from all three years Sierra has ranked these institutions shows the ratings aren’t consistent, either. Only two—Middlebury and Oberlin—made the top 10 all three years. Yale, a model of sustainability, has never hit the top of the list (it’s #14 this year). And Warren Wilson, a school that lives and breathes environmentalism, ranked #3 in 2007 but dropped to #18 this year.

As a result, it’s not very credible, even though the Sierra Club is a highly respected organization. (Full disclosure: I’m a member.)

Part of this can be explained by the explosion of schools that are making sustainability a priority. There are simply lots more colleges and universities making green claims. Now more than ever, those that communicate best about their programs—providing full information, with clear measures of success—will get the recognition.

I’ve found that educational institutions are uncomfortable about trumpeting their work generally and about marketing in particular. But they shouldn’t be. There’s a lot at stake. Both parents and prospective students care a lot about whether a school is green, with two-thirds of them saying the it would influence their decision to apply or attend, according to Princeton Review’s 2009 “College Hopes and Worries” survey.