This study investigates the relationship between School Library and Students' achievement on a population sample of 9896 Schools. Many international researches confirmed the importance of the School Library for the Students learning. Recently the IEA PIRLS survey has revealed a positive relationship between the Reading comprehension performance and the size of the School Library collection. In this paper, we verify the relation between the results of INVALSI tests in Italian and Mathematics--on school grades 5,8,10--with the presence and functioning of the School Library. The information on the School Library comes from the School Questionnaire compiled by the School Principal in the course of the Self-evaluation Report. The analysis confirm a positive relationship in each school grade and in both subjects of investigation.