The effect of individualized digital practice at home on math skills-Evidence from a two-stage experiment on whether and why it works

•Digital numeracy practice at home increase numeracy performance significantly.•The effectiveness of the tool mainly stems from its individualized nature.•Implementation prospects are good and costs are relatively low.

This paper analyses an experiment on the effect of an individualized, digital practice tool on numeracy skills for 337 seventh grade students. The first stage of the experiment shows that offering students the opportunity to practice numeracy digitally at home (intent-to-treat) leads to a substantial and significant increase in numeracy performance growth. The second stage reveals that the effectiveness of the tool mainly stems from its individualized nature. With good implementation prospects and relatively low costs, the consequences are discussed to be potentially large.