In 2005, the Austrian government committed all schools to develop school policies supporting the learning of their students. One purpose of the paper is to seek evidence for the effectiveness of this governmental action. A second purpose is to suggest a special kind of multilevel model which can be applied to longitudinal data at the school level when the outcome measure of interest is assessed at the individual student level. Analyses are based on 2 nation-wide educational standards assessments (2012 and 2015) and a preceding baseline assessment including n = 267 primary schools (2010). Results show that the implementation of support strategies by schools significantly moderated the increase in mathematic achievement between 2010 and 2013, but not in reading achievement between 2010 and 2015. However, the increase in reading achievement was moderated by the provision of additional courses for low-achieving students and for students with a foreign first language.