Question 2: participant characteristics
word reading fluency)
SEPARATION
As for the second research question about participant characteristics, we asked whether there are certain subgroups of children who benefit more from GraphoGame-NL exposure than others and hypothesised that poor performers would benefit more. However, the effects relating to gaming condition were mostly main effects, indicating that there were no systematic differences between participants’ proficiency levels across the three experimental groups. The only exception, pointing in the opposite direction to our hypothesis, was that few children who performed above average in phonological awareness skills at pre-test who were comparatively faster readers when they had above average exposure to the reading game. We also anticipated that certain subgroups of children, like those at familial risk or those speaking a different language at home, might perform worse at pre-test and exhibit a different outcome from exposure to the game, but this was not evident in our findings.Most studies use an inclusion criterion based on scores in reading-related tests (To prevent such sampling bias in the present study, we invited all children from 16 classrooms to play, independent of their performance on reading-related tasks and investigated the effect of pre-test scores on training-induced skill improvement. Our approach was unintentionally strengthened further because of the large pre-test differences between the Dutch and Belgian children in our sample. These differences appear to stem from the different preschool systems, where Belgium has a stricter separation of pre-school and school, compared to the more gradual transition into formal instruction from four years of age onwards in the Netherlands. Similar differences between these two neighbouring countries have been observed in early numeracy skills (At first sight, one could argue that, due to the absence of interactions of pre-test scores and outcome, the intervention was equally effective for all children. However, when comparing results stratified by country, it is apparent that the weaker beginning readers in Belgium showed more intervention effects (both in letter-sound knowledge and word reading fluency), whereas in the more advanced Dutch sample, we found fewer effects (limited to grapheme-phoneme correspondence automation). This can be taken as evidence that individual starting levels matter for GraphoGame‑NL intervention outcomes, in line with most previous studies. Training poor performers at an early stage in their literacy development usually yields group-wide benefits in easily trainable skills like letter knowledge (