Laying off librarians has a negative effect on fourth grade reading scores (2004 to 2009): "fewer librarians translated to lower performance—or a slower rise in scores—on standardized tests." Most important, Lance and Hofshine present evidence showing that the negative effect was due specifically to laying off librarians, not overall staff changes.
"We found that 19 of the 26 states that gained librarians saw an average 2.2 percent rise in their National Assessment of Educational Progress (NAEP) fourth-grade reading scores. Meanwhile, 9 of the 24 states that lost librarians had a 1 percent rise … the increase in scores of states that gained librarians was two times that of states that lost librarians. Scores remained unchanged for 6 states that gained librarians and 12 that lost librarians. Three states that lost librarians had an average decline of -1 percent, and one state that gained librarians experienced a -0.5 percent decline in scores."
" … the magnitude and significance of the relationship between librarian staffing and test performance was reduced only very slightly when taking into account overall staff changes in schools … Whether a school had a librarian remained an important factor in reading test performance, regardless of what was happening with overall staffing numbers."
Correlation between percent change in school librarians and percent change in reading scores for all students: r = .567. Correlation when controlled for percent change in total school staff: r = .562 (partial correlation).
Lance, K., & Hofshine, L. (2011). Something to Shout About: New research shows that more librarians means higher reading scores. School Library Journal, Sept. 1.
Information provided by Stephen Krashen