Background: There is increasing recognition of the contribution of affective factors such as motivation to the development of reading competence. Reading activity is theorised to mediate associations between motivation and achievement, but this has been tested empirically only rarely. Method: This study employed structural equation modelling to test a hypothesised model of relations between the reading self-concept, intrinsic motivation, activity and achievement of a sample of 4,067 grade 6 students in Ireland and to explore whether the relations were moderated by gender or socioeconomic status (SES). Results: Intrinsic motivation and self-concept were significantly associated with reading activity, which, in turn, significantly predicted reading achievement. Girls had higher intrinsic motivation and reading activity than boys, but there was no gender difference in reading self-concept. High-SES students had higher reading self-concept, intrinsic motivation and activity than low-SES and medium-SES students. The strength of the associations among the constructs under study did not vary by gender or SES. Conclusions: Findings suggest that efforts aimed at increasing students' intrinsic reading motivation may lead to increased reading activity and reading competence, irrespective of gender or SES.