Readability formulae targeting children have been developed, but their appropriateness can still be improved, for example by taking into account suffixation. Literacy research has identified the suffixation phenomenon makes children’s reading difficult, so we analyze the effectiveness of suffixation within the context of readability. Our analysis finds that suffixation is potentially effective for readability assessment. Moreover, we find that existing readability formulae fail to discern lower grade levels for texts from different existing corpora.