Abstract
Although many educational programs have demonstrated the potential to increase student learning, few examples of successful scaling exist. We study the scalability of a parent-aimed reading program that has shown promising results in an experiment within a local government. Using a nationwide experiment among the full population of 2nd-grade children in Danish public schools (n=51,312), we find that the program is less effective at large scale. We provide evidence on potential explanations for the lack of scalability, which suggests that implementation fidelity is the most important barrier to successfully scaling this type of educational interventions.