Alternative splits of performance for voxel-wise statistical comparison

As indicated in the main manuscript, group definition are often based on arbitrary cut-offs on behavioural measures. In addition to the comparison between children scoring two or more standard deviations below the age-expected mean, alternative group comparisons are presented here. These are based on percentile splits of the data in order to maintain equivalent sample sizes. The characteristics of these groups are presented in  Table  \ref{table:reading_characteristics} for characteristics of groups split by reading performance and Table \ref{table:reading_characteristics} for characteristics of groups split by maths performance.