This repository contains the data from a cluster randomized trial testing the effectiveness of a digital game-based learning tool for beginning readers of Dutch at the onset of first grade. The study offered participation to all 312 children enrolled into 16 classrooms at 8 schools in Groningen, The Netherlands and Ghent in the Dutch-speaking part of Belgium. Randomization took place at the classroom level into treatment groups of the reading intervention (GraphoGame-NL), an active control group playing math content in the same gaming framework (GraphoGame-NL-Math) and a passive control group only attending classroom activities. The intervention consisted of 10 to 15 minutes of daily playing during school time for a period of up to 7 weeks. We collected data on nonverbal intelligence, reading fluency, phonological skills, and rapid automatized naming. In addition, we measured written lexical decision and letter speech sound association with purpose built in-game levels. In this repository we deposit the data ...