Additional covariates
handedness, dyslexia
To investigate sample characteristics, the following independent variables were available from parental questionnaires: age in years, binary sex (female, male), handedness (left, right, mixed), familial risk for dyslexia (yes, no), and language spoken at home (Dutch or a foreign language). To evaluate the influence of exposure to the game, we extracted six covariates related to the individual progress children made within the game: number of sessions played, hours played, levels played, number of items seen on the screen, given responses, and maximum level achieved at the end of the intervention. For the analysis of in-game assessments, we also extracted properties of the gameplay that are not relevant for our research questions (While there should be no unmeasured confounding in a randomised trial when randomisation was successful, adding prognostic covariates can increase power and yield more precise estimates (