Why should children read in their leisure time? Reading may contribute to the acquisition of reading literacy and may foster integral human development. However, there has been a scarcity of research on determinants of leisure time reading among elementary school students, especially regarding environmental aspects. In this article, the authors report on the development of a differentiated questionnaire regarding these determinants. Based on a previous series of qualitative and quantitative pilot studies, a study with 980 elementary school students was conducted, applying scales based on behavioral beliefs (motivation in action, thematically congruent consequences, and thematically incongruent costs and benefits), normative beliefs (subjective norm), and control beliefs (self-efficacy and controllability) as predictors of leisure time reading. After excluding motivation in action from analysis because of multicollinearity problems, the variables thematically incongruent costs and benefits, self-efficacy, and controllability explained 50% of variance in the criterion reading frequency. Analyses of covariance indicated that children, especially daughters, of mothers with high educational attainment showed significantly more leisure time reading. The benefits of focusing on students' beliefs and of including environmental aspects in research on leisure time reading are discussed.