Persistent grammatical difficulties in Specific Language Impairment Deficits in knowledge or in knowledge implementation?

This study examines the grammatical abilities of children and adolescents with Specific Language Impairment (SLI). There were two research goals. Firstly, the persistence of grammatical problems over time was examined by comparing a younger group of children with SLI and an older group of adolescents with SLI. Secondly, this study explored whether difficulties in the grammatical domain in SLI purely reflect a grammatical deficit or may partly stem from problems in the implementation of grammatical knowledge due to problems in information processing. In the grammatical production tasks, the complexity of the linguistic context was therefore varied to examine whether this would cause a (larger) decrease in scores in the SLI groups. In addition, the link between variability in performance and processing abilities was examined.
On the basis of the outcomes this book makes two major claims. Firstly, grammatical problems in SLI are persistent into adolescence. For some grammatical aspects such as grammatical gender, fossilization seemed to take place before children reach adolescence. Other aspects (e.g. verb inflection), had clearly been acquired by adolescence but differences between SLI and typical development (TD) in the amount of errors still remained. Secondly, grammatical performance in SLI was affected by the linguistic context in which grammatical knowledge had to be implemented. Such effects were small or absent in the TD groups. The effect of context was related to the verbal processing abilities of the groups. Even when grammatical knowledge has been acquired, individuals with SLI are not always able to implement this knowledge in performance.