Acquisition of reading comprehension is a major aim of primary education. However, research on its development and effective methods for its enhancement are scarce. This interlinked project contains three part-projects aiming at a common longitudinal data base and a common intervention study. In the longitudinal study the cognitive and non-cognitive skills are examined that foster reading comprehension development and its interplay with vocabulary acquisition. Effects of working memory, syntactic awareness, comprehension skills, reading strategies and motivation for reading are considered. In the intervention study it is examined whether an intervention for reading comprehension should be focused on reading strategies, or on vocabulary acquisition. Interventions implementing each method and an intervention that combines these methods are compared. The longitudinal study serves as a control group. Finally, the moderating effects of the teacher (quality of instruction, relations with students) and of specific child characteristics on the effects of the interventions are considered.