Reading skills are considered an important lever for success in school and active participation in society. They are positively associated with reading motivation, reading self-concept, reading frequency, and behavioral engagement in reading (e.g., time, effort), variables that tend to decline as students move from elementary to secondary school. Few studies have yet compared the contributions of reading support from teachers, parents, and friends to each of these variables among students of different age groups. In this multicohort correlational study, students (n = 1246) in grades 4, 6, 8, and 10 completed a questionnaire measuring the reading support they perceived receiving from three social agents (teacher, parents, and friends) as well as variables related to reading in academic and recreational contexts. The data collected were used to evaluate the construct relevance and predictive validity of the questionnaire. The results suggest that: (1) Reading support can be conceptualized in nine dimensions defined according to the source that provides it (e.g., teachers) and the type to which it corresponds (e.g., relatedness support); (2) secondary school students overall consider that they receive less reading support than do elementary school students; (3) reading support from teacher has unique contributions to certain variables measured in the academic context without, however, having as many positive contributions as parents in this context; (4) reading support provided by parents and friends is important in both reading contexts, particularly in the recreational context. Methodological, theoretical, and practical implications are discussed.