This site is worth keeping an eye on if you are looking for recent research on school libraries:

Washington State School Library Impact Study: the full report

Curated by Lyn Hay

See the new study summarized by Carolyn Sun, in School Library Journal, May 26, 2015

“School library programs are positive predictors of student success that poverty cannot suppress,” Lance says. “Some people think that poorer students are going to do poorly in school no matter what we do. The findings of these studies challenge that by showing that even poorer students do better in the presence of strong school library programs.” …

The Washington study takes this work a step further, incorporating analysis regarding the quality of library services. While 96.7 percent of the survey respondents reported having an on-site library facility, just having a library facility is not enough, according to the report. The library must have a high-quality program, determined by specific factors, and related instructional services in order to positively influence student achievement…