This dataset consisting of longitudinal data gathered in the BRXXX project, which aimed at investigating the effectiveness of online mathematics mini-games in enhancing primary school students’ multiplicative reasoning ability. The dataset includes data of 719 students from 35 primary schools in the Netherlands, who were followed from end Grade 1 (Dutch “groep 3”) to end Grade 3 (Dutch “groep 5”. Participating schools were randomly divided over three experimental conditions (playing at school, at home, or at home with debriefing at school) and a control group. Tests of multiplicative ability were administered at the end of Grade 1 (pretest) and the end of Grade 2 and Grade 3 (posttests), measuring students’ knowledge of multiplication number facts, their skills in calculating multiplicative problems, and their insight in multiplicative number relations. In addition to the scores on these tests, the dataset includes measures of gameplay behavior, i.e. the time and effort students put in the games, and some student background variables.