I've recently run across two resources that school librarians will want to study.
First, have you seen the great data that's come out of Colorado? There's the infographic shown above, as well as lots of links to presentations, best practices, data, and more at the State Library's site.
Second, there's been a large study going on at Rutgers University in New Jersey, under the auspices of CiSSL. The Center for International Scholarship in School Libraries already has data on its website from Phases 1 & 2 of ongoing studies about school library value. (CiSSL is "the leading international center dedicated to school libraries worldwide, provides an arena for the international community of school library scholars and practitioners to generate produce and share a substantial body of rigorous research on the dynamics and impacts of school libraries on student learning.') CiSSL has just wrapped up a summer conference, so look for more info from the researchers soon.
I'm sure there are other great K-12 resources out there; these are just two that have gotten my attention lately. What are your favorites? Share them here!