The moderate performances of German students in international large-scale assessments resulted in a nationwide school reform aiming at a comprehensive implementation of all-day schools. Within the last decade, the number of schools, which provide extracurricular, all-day programs for their students, more than tripled (KMK, 2012). Educationally, all-day schools are considered to be one instrument to enhance students’ learning by increasing their domain-specific competencies and by reducing educational inequality (Holtappels, 2009). However, only little is known about the effects of full-time schooling – especially when compared to part-time schooling. First results located on the organizational level of schools (Reinders et al., 2010; Radisch, Klieme & Bos, 2006; Strietholt et al., subm.) indicate that the reading competencies of students in all-day schools do not differ from the competencies of students who are taught in half-day schools. Even though global effects of different organizational school-types are not found, it can be assumed that the individual participation of students in extracurricular learning opportunities can be conducive for the students’ domain-specific learning. Based on data from PIRLS and TIMSS 2011 the present paper investigates in how far the participation in all-day school programs is related to the students’ achievement in mathematics, science, and reading.