The development of morphological awareness and vocabulary: What influences what?

The awareness of words' morphological structure has been thought to allow generalizing meaning to other, similarly constructed words. Conversely, a large vocabulary is thought to facilitate the recognition of words' morphological regularities, thereby contributing to morphological awareness. For this reason, morphological awareness and vocabulary have been suggested to be reciprocally associated across development. We followed 242 (girls = 119) Norwegian preschoolers (M age = 5.5 years) from preschool through Grade 2 and examined the cross-lagged relations between morphological awareness (inflections and derivations) and vocabulary (receptive and expressive). Our results confirm that the traditional cross-lagged panel model shows significant cross-lagged relations between morphological awareness and vocabulary, as previous studies have shown. However, no cross-lagged relations were found when we accounted for longitudinal measured stability through a cross-lagged panel model with lag-2 paths or unmeasured stability through the random intercept cross-lagged panel model. We found that approximately 50% of the variation in morphology and vocabulary was due to highly stable and invariant factors across grades. We discuss how the significant cross-lagged relations found in previous studies could have been due to their not accounting for the right type of stability when using longitudinal panel data.