Longitudinal relations between phonological and grammatical development of young children with developmental language disorder

Most children with a developmental language disorder (DLD) have persistent grammatical difficulties, and a considerable subgroup of these children also experience difficulties in their speech production development. Research suggests that speech and language development are related, but what this relation looks like is unclear. We examined whether phonological and grammatical complexity and accuracy scores of 3- to 6-year-old children with DLD are related over time. We included 37 children with DLD (mean age T1 = 4;2 (SD = 1;0), range: 2;9-6;0) who received intervention in a clinical setting. Picture-naming tasks and language sample analyses were conducted four times at 3-month intervals within a 9-month period. We conducted a growth curve analysis on outcome measures for phonological and grammatical complexity and accuracy. Our results show that the children with DLD improve in phonological and grammatical complexity and accuracy, and this improvement can be captured by a linear function. The phonological and grammatical scores within each dimension were related at T1; children with higher scores in phonological complexity/accuracy were likely to have higher scores in grammatical complexity/accuracy as well. However, this relation becomes weaker within the 9-month follow-up. Therefore, our results indicate that children who improve in one domain do not necessarily improve at the same rate in the other domain. This study provides new insights into how the phonological and grammatical developmental trajectories of children with DLD are related. This might help clinicians in selecting interventions targeting one or both of these domains.